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multi_agent_system_mod.f90

Timestamp:

Oct 21, 2020 2:55:41 PM (4 years ago)

Author:

raasch

Message:

files re-formatted to follow the PALM coding standard

File:

: 1 edited

palm/trunk/SOURCE/multi_agent_system_mod.f90 (modified) (38 diffs)

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: Unmodified
: Added
: Removed

palm/trunk/SOURCE/multi_agent_system_mod.f90

-                      r4623
+                      r4753
 !> @file multi_agent_system_mod.f90
+!--------------------------------------------------------------------------------!
+! This file is part of PALM-4U.
+!
+! PALM-4U is free software: you can redistribute it and/or modify it under the
+! terms of the GNU General Public License as published by the Free Software
+! Foundation, either version 3 of the License, or (at your option) any later
+! version.
+!
+! PALM-4U is distributed in the hope that it will be useful, but WITHOUT ANY
+! WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
+! A PARTICULAR PURPOSE.  See the GNU General Public License for more details.
+!
+! You should have received a copy of the GNU General Public License along with
+! PALM. If not, see <http://www.gnu.org/licenses/>.
+!--------------------------------------------------------------------------------------------------!
+! This file is part of the PALM model system.
+!
+! PALM is free software: you can redistribute it and/or modify it under the terms of the GNU General
+! Public License as published by the Free Software Foundation, either version 3 of the License, or
+! (at your option) any later version.
+!
+! PALM is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the
+! implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General
+! Public License for more details.
+!
+! You should have received a copy of the GNU General Public License along with PALM. If not, see
+! <http://www.gnu.org/licenses/>.
+!
 ! Copyright 2016-2020 Leibniz Universitaet Hannover
 !------------------------------------------------------------------------------!
+!--------------------------------------------------------------------------------------------------!
+!
 ! Current revisions:
 …
 ! -----------------
 ! $Id$
+! file re-formatted to follow the PALM coding standard
+!
+! 4623 2020-07-24 08:42:02Z raasch
 ! some switches calculated explicitly to avoid compiler warnings
+!
+!
 ! 4481 2020-03-31 18:55:54Z maronga
 ! bugfix: cpp-directives for serial mode added
+!
+!
 ! 4346 2019-12-18 11:55:56Z motisi
+! Removed wall_flags_static_0 from USE statements as it's not used within
+! the module
+!
+! Removed wall_flags_static_0 from USE statements as it's not used within the module
+!
 ! 4329 2019-12-10 15:46:36Z motisi
 ! Renamed wall_flags_0 to wall_flags_static_0
+!
+!
 ! 4307 2019-11-26 14:12:36Z maronga
 ! Activated output of iPT
+!
+!
 ! 4182 2019-08-22 15:20:23Z scharf
 ! Corrected "Former revisions" section
+!
+!
 ! 4168 2019-08-16 13:50:17Z suehring
 ! Replace function get_topography_top_index by topo_top_ind
+!
+!
 ! 3987 2019-05-22 09:52:13Z kanani
 ! Introduce alternative switch for debug output during timestepping
+!
+!
 ! 3885 2019-04-11 11:29:34Z kanani
 ! Changes related to global restructuring of location messages and introduction
 ! of additional debug messages
+!
+! Changes related to global restructuring of location messages and introduction  of additional debug
+! messages
+!
 ! 3876 2019-04-08 18:41:49Z knoop
 ! replaced nspec by nvar: only variable species should bconsidered, fixed species are not relevant
+!
+! replaced nspec by nvar: only variable species should bconsidered, fixed species are not relevant
+!
 ! 3766 2019-02-26 16:23:41Z raasch
 ! save attribute added to local targets to avoid outlive pointer target warning
+!
+!
 ! 3665 2019-01-10 08:28:24Z raasch
 ! unused variables removed
+!
+!
 ! 3159 2018-07-20 11:20:01Z sward
 ! Initial revision
+!
+!
+!
+!
 ! Authors:
 …
 ! Description:
 ! ------------
+!> Multi Agent System for the simulation of pedestrian movement in urban
+!> environments
+!------------------------------------------------------------------------------!
+!> Multi Agent System for the simulation of pedestrian movement in urban environments
+!--------------------------------------------------------------------------------------------------!
  MODULE multi_agent_system_mod
     USE, INTRINSIC ::  ISO_C_BINDING
     USE basic_constants_and_equations_mod,                                     &
+    USE basic_constants_and_equations_mod,                                                         &
         ONLY:  pi
     USE control_parameters,                                                    &
         ONLY:  biometeorology,                                                 &
                debug_output_timestep,                                          &
                dt_3d,                                                          &
                dt_write_agent_data,                                            &
                message_string,                                                 &
+    USE control_parameters,                                                                        &
+        ONLY:  biometeorology,                                                                     &
+               debug_output_timestep,                                                              &
+               dt_3d,                                                                              &
+               dt_write_agent_data,                                                                &
+               message_string,                                                                     &
                time_since_reference_point
     USE cpulog,                                                                &
+    USE cpulog,                                                                                    &
         ONLY:  cpu_log, log_point, log_point_s
     USE grid_variables,                                                        &
+    USE grid_variables,                                                                            &
         ONLY:  ddx, ddy, dx, dy
+    USE indices,                                                               &
+        ONLY:  nx, nxl, nxlg, nxr, nxrg, ny, nyn, nyng, nys, nysg, nzb,        &
+               topo_top_ind
+    USE random_function_mod,                                                   &
+    USE indices,                                                                                   &
+        ONLY:  nx, nxl, nxlg, nxr, nxrg, ny, nyn, nyng, nys, nysg, nzb, topo_top_ind
+    USE random_function_mod,                                                                       &
         ONLY:  random_function
 …
     USE pegrid
+    INTEGER(iwp), PARAMETER ::  max_number_of_agent_groups = 100  !< maximum allowed number of agent groups
+    INTEGER(iwp), PARAMETER ::  nr_2_direction_move = 10000       !< parameter for agent exchange
+    INTEGER(iwp), PARAMETER ::  phase_init    = 1                 !< phase parameter
+    INTEGER(iwp), PARAMETER ::  phase_release = 2                 !< phase parameter
     CHARACTER(LEN=15) ::  bc_mas_lr = 'absorb'  !< left/right boundary condition
     CHARACTER(LEN=15) ::  bc_mas_ns = 'absorb'  !< north/south boundary condition
+    INTEGER(iwp) ::  agt_path_size = 15                !< size of agent path array
     INTEGER(iwp) ::  deleted_agents = 0                !< number of deleted agents per time step
     INTEGER(iwp) ::  dim_size_agtnum_manual = 9999999  !< namelist parameter (see documentation)
 …
     INTEGER(iwp) ::  number_of_agent_groups = 1        !< namelist parameter (see documentation)
     INTEGER(iwp) ::  sort_count_mas = 0                !< counter for sorting agents
-    INTEGER(iwp) ::  agt_path_size = 15                !< size of agent path array
     INTEGER(iwp) ::  step_dealloc_mas = 100            !< namelist parameter (see documentation)
     INTEGER(iwp) ::  total_number_of_agents            !< total number of agents in the whole model domain
-    INTEGER(iwp), PARAMETER ::  NR_2_direction_move = 10000 !< parameter for agent exchange
-    INTEGER(iwp), PARAMETER ::  PHASE_INIT    = 1           !< phase parameter
-    INTEGER(iwp), PARAMETER ::  PHASE_RELEASE = 2           !< phase parameter
-    INTEGER(iwp), PARAMETER ::  max_number_of_agent_groups = 100 !< maximum allowed number of agent groups
     INTEGER(iwp), DIMENSION(:,:), ALLOCATABLE ::  agt_count         !< 3d array of number of agents of every grid box
 …
     INTEGER(iwp), DIMENSION(:,:), ALLOCATABLE ::  top_top_s         !< k-index of first s-gridpoint above topography
     INTEGER(iwp), DIMENSION(:,:), ALLOCATABLE ::  top_top_w         !< k-index of first v-gridpoint above topography
+    INTEGER(iwp), DIMENSION(:,:), ALLOCATABLE ::  obstacle_flags    !< flags to identify corners and edges of topography that cannot be crossed by agents
+    INTEGER(iwp), DIMENSION(:,:), ALLOCATABLE ::  obstacle_flags    !< flags to identify corners and edges of topography that cannot
+                                                                    !< be crossed by agents
     LOGICAL ::  deallocate_memory_mas = .TRUE.          !< namelist parameter (see documentation)
 …
     END TYPE agent_type
+    TYPE(agent_type)                        ::  zero_agent           !< zero agent to avoid weird thing
     TYPE(agent_type), DIMENSION(:), POINTER ::  agents               !< Agent array for this grid cell
-    TYPE(agent_type)                        ::  zero_agent           !< zero agent to avoid weird thing
 #if defined( __parallel )
-    TYPE(agent_type), DIMENSION(:), ALLOCATABLE ::  move_also_north  !< for agent exchange between PEs
-    TYPE(agent_type), DIMENSION(:), ALLOCATABLE ::  move_also_south  !< for agent exchange between PEs
     TYPE(agent_type), DIMENSION(:), ALLOCATABLE ::  agt_gh_l         !< ghost layer left of pe domain
     TYPE(agent_type), DIMENSION(:), ALLOCATABLE ::  agt_gh_n         !< ghost layer north of pe domain
     TYPE(agent_type), DIMENSION(:), ALLOCATABLE ::  agt_gh_r         !< ghost layer right of pe domain
     TYPE(agent_type), DIMENSION(:), ALLOCATABLE ::  agt_gh_s         !< ghost layer south of pe domain
+    TYPE(agent_type), DIMENSION(:), ALLOCATABLE ::  move_also_north  !< for agent exchange between PEs
+    TYPE(agent_type), DIMENSION(:), ALLOCATABLE ::  move_also_south  !< for agent exchange between PEs
 #endif
+!
 …
 !------------------------------------------------------------------------------!
+!--------------------------------------------------------------------------------------------------!
 ! Description:
 ! ------------
 !> Multi Agent System:
 !> executes a number of agents sub-timesteps until the model timestep is reached.
 !> The agent timestep is usually smaller than the model timestep
 !------------------------------------------------------------------------------!
+!> The agent timestep is usually smaller than the model timestep.
+!--------------------------------------------------------------------------------------------------!
  SUBROUTINE multi_agent_system
     USE biometeorology_mod,                                                    &
         ONLY:  bio_calc_ipt,                                                   &
                bio_calculate_mrt_grid,                                         &
+    USE biometeorology_mod,                                                                        &
+        ONLY:  bio_calc_ipt,                                                                       &
+               bio_calculate_mrt_grid,                                                             &
                bio_get_thermal_index_input_ij
 …
     INTEGER(iwp)       ::  js                 !< counter
     INTEGER(iwp), SAVE ::  mas_count = 0      !< counts the mas-calls
+    INTEGER(iwp)                :: a     !< agent iterator
+    !-- local meteorological conditions
+    REAL(wp)                    :: tmrt  !< mean radiant temperature        (degree_C)
+    REAL(wp)                    :: ta    !< air temperature                 (degree_C)
+    REAL(wp)                    :: vp    !< vapour pressure                 (hPa)
+    REAL(wp)                    :: v     !< wind speed    (local level)     (m/s)
+    REAL(wp)                    :: pair  !< air pressure                    (hPa)
+    INTEGER(iwp)       ::  a                  !< agent iterator
+!
+!-- local meteorological conditions
+    REAL(wp) ::  pair  !< air pressure                    (hPa)
+    REAL(wp) ::  ta    !< air temperature                 (degree_C)
+    REAL(wp) ::  tmrt  !< mean radiant temperature        (degree_C)
+    REAL(wp) ::  v     !< wind speed    (local level)     (m/s)
+    REAL(wp) ::  vp    !< vapour pressure                 (hPa)
 …
     CALL cpu_log( log_point(9), 'mas', 'start' )
+!
 !-- Initialize variables for the next (sub-) timestep, i.e., for marking
 !-- those agents to be deleted after the timestep
+!-- Initialize variables for the next (sub-) timestep, i.e., for marking those agents to be deleted
+!-- after the timestep
     deleted_agents = 0
     agent_substep_time = 0.0_wp
 …
     IF ( time_arel >= dt_arel  .AND.  end_time_arel > time_since_reference_point )  THEN
+       CALL mas_create_agent(PHASE_RELEASE)
+!
+!--    The MOD function allows for changes in the output interval with
+!--    restart runs.
+       CALL mas_create_agent( phase_release )
+!
+!--    The MOD function allows for changes in the output interval with restart runs.
        time_arel = MOD( time_arel, MAX( dt_arel, dt_3d ) )
 …
+!
 !-- Timestep loop for agent transport.
 !-- This loop has to be repeated until the transport time of every agent
 !-- (within the total domain!) has reached the LES timestep (dt_3d).
 !-- Timestep scheme is Euler-forward
+!-- This loop has to be repeated until the transport time of every agent (within the total domain!)
+!-- has reached the LES timestep (dt_3d).
+!-- Timestep scheme is Euler-forward.
     DO
+!
 …
           CALL mas_data_output_agents ( first_call )
 #else
           WRITE( message_string, * ) 'NetCDF is needed for agent output. ',    &
+          WRITE( message_string, * ) 'NetCDF is needed for agent output. ',                        &
                                      'Set __netcdf in compiler options'
           CALL message( 'multi_agent_system', 'PA0071', 1, 2, 0, 6, 0 )
 …
        ENDIF
+!
 !--    Flag is true by default, will be set to false if an agent has not yet
 !--    reached the model timestep
+!--    Flag is true by default, will be set to false if an agent has not yet reached the model
+!--    timestep.
        grid_agents(:,:)%time_loop_done = .TRUE.
 …
              agents(1:number_of_agents)%agent_mask = .TRUE.
+!
 !--          Initialize the variable storing the total time that an agent
 !--          has advanced within the timestep procedure
+!--          Initialize the variable storing the total time that an agent has advanced within the
+!--          timestep procedure.
              IF ( first_loop_stride )  THEN
                 agents(1:number_of_agents)%dt_sum = 0.0_wp
              ENDIF
+!
+!--          Initialize the switch used for the loop exit condition checked
+!--          at the end of this loop. If at least one agent has failed to
+!--          reach the LES timestep, this switch will be set false in
+!--          mas_transport.
+!--          Initialize the switch used for the loop exit condition checked at the end of this loop.
+!--          If at least one agent has failed to reach the LES timestep, this switch will be set
+!--          false in mas_transport.
              dt_3d_reached_l_mas = .TRUE.
+!
 …
              CALL mas_timestep
+!
 !--          Delete agents that have been simulated longer than allowed
+!--          Delete agents that have been simulated longer than allowed.
              CALL mas_boundary_conds( 'max_sim_time' )
+!
 !--          Delete agents that have reached target area
+!--          Delete agents that have reached target area.
              CALL mas_boundary_conds( 'target_area' )
+!
+!---         If not all agents of the actual grid cell have reached the
+!--          LES timestep, this cell has to to another loop iteration. Due to
+!--          the fact that agents can move into neighboring grid cell,
+!--          these neighbor cells also have to perform another loop iteration
+!--          If not all agents of the actual grid cell have reached the LES timestep, this cell has
+!--          to do another loop iteration. Due to the fact that agents can move into neighboring
+!--          grid cell, these neighbor cells also have to perform another loop iteration.
              IF ( .NOT. dt_3d_reached_l_mas )  THEN
                 js = MAX(nys,j-1)
 …
+!
 !--    Find out, if all agents on every PE have completed the LES timestep
 !--    and set the switch corespondingly
+!--    Find out, if all agents on each PE have completed the LES timestep and set the switch
+!--    corespondingly.
        dt_3d_reached_l_mas = ALL(grid_agents(:,:)%time_loop_done)
 #if defined( __parallel )
        IF ( collective_wait )  CALL MPI_BARRIER( comm2d, ierr )
        CALL MPI_ALLREDUCE( dt_3d_reached_l_mas, dt_3d_reached_mas, 1, MPI_LOGICAL, &
                            MPI_LAND, comm2d, ierr )
+       CALL MPI_ALLREDUCE( dt_3d_reached_l_mas, dt_3d_reached_mas, 1, MPI_LOGICAL,  MPI_LAND,      &
+                           comm2d, ierr )
 #else
        dt_3d_reached_mas = dt_3d_reached_l_mas
 …
        CALL mas_eh_exchange_horiz
+!
+!--    Pack agents (eliminate those marked for deletion),
+!--    determine new number of agents
+!--    Pack agents (eliminate those marked for deletion), determine new number of agents
        CALL mas_ps_sort_in_subboxes
        CALL cpu_log( log_point_s(18), 'mas_move_exch_sort', 'stop' )
+!
 !--    Initialize variables for the next (sub-) timestep, i.e., for marking
 !--    those agents to be deleted after the timestep
+!--    Initialize variables for the next (sub-) timestep, i.e., for marking those agents to be
+!--    deleted after the timestep
        deleted_agents = 0
 …
+!
 !--             Determine local meteorological conditions
+                CALL bio_get_thermal_index_input_ij ( .FALSE., i, j, ta, vp,  &
+                                                      v, pair, tmrt )
+                CALL bio_get_thermal_index_input_ij ( .FALSE., i, j, ta, vp, v, pair, tmrt )
                 DO  a = 1, number_of_agents
 …
 !--                Calculate instationary thermal indices based on local tmrt
                    CALL bio_calc_ipt ( ta, vp, v, pair, tmrt,                 &
                                        agents(a)%dt_sum,                      &
                                        agents(a)%energy_storage,              &
                                        agents(a)%clothing_temp,               &
                                        agents(a)%clo,                         &
                                        agents(a)%actlev,                      &
                                        agents(a)%age_years,                   &
                                        agents(a)%weight,                      &
                                        agents(a)%height,                      &
                                        agents(a)%work,                        &
                                        agents(a)%sex,                         &
+                   CALL bio_calc_ipt ( ta, vp, v, pair, tmrt,                                      &
+                                       agents(a)%dt_sum,                                           &
+                                       agents(a)%energy_storage,                                   &
+                                       agents(a)%clothing_temp,                                    &
+                                       agents(a)%clo,                                              &
+                                       agents(a)%actlev,                                           &
+                                       agents(a)%age_years,                                        &
+                                       agents(a)%weight,                                           &
+                                       agents(a)%height,                                           &
+                                       agents(a)%work,                                             &
+                                       agents(a)%sex,                                              &
                                        agents(a)%ipt )
                 END DO
 …
  END SUBROUTINE multi_agent_system
 !------------------------------------------------------------------------------!
+!--------------------------------------------------------------------------------------------------!
 ! Description:
 ! ------------
+!> Calculation of the direction vector from each agent to its current
+!> intermittent target
+!------------------------------------------------------------------------------!
+    SUBROUTINE mas_agent_direction
+       IMPLICIT NONE
+       LOGICAL ::  path_flag !< true if new path must be calculated
+       INTEGER(iwp) ::  n  !< loop variable over all agents in a grid box
+       INTEGER(iwp) ::  pc !< agent path counter
+       REAL(wp) ::  abs_dir         !< length of direction vector (for normalization)
+!       REAL(wp) ::  d_curr_target   !< rounding influence expressed as x speed component
+!       REAL(wp) ::  d_prev_target   !< rounding influence expressed as x speed component
+       REAL(wp) ::  dir_x           !< direction of agent (x)
+       REAL(wp) ::  dir_y           !< direction of agent (y)
+!       REAL(wp) ::  dist_round = 3. !< distance at which agents start rounding a corner
+       REAL(wp) ::  dtit            !< distance to intermittent target
+!       REAL(wp) ::  round_fac  = 0.2 !< factor for rounding influence
+!       REAL(wp) ::  speed_round_x   !< rounding influence expressed as x speed component
+!       REAL(wp) ::  speed_round_y   !< rounding influence expressed as x speed component
+!
+!--    loop over all agents in the current grid box
+       DO n = 1, number_of_agents
+          path_flag = .FALSE.
+!> Calculation of the direction vector from each agent to its current intermittent target.
+!--------------------------------------------------------------------------------------------------!
+ SUBROUTINE mas_agent_direction
+    IMPLICIT NONE
+    LOGICAL ::  path_flag  !< true if new path must be calculated
+    INTEGER(iwp) ::  n   !< loop variable over all agents in a grid box
+    INTEGER(iwp) ::  pc  !< agent path counter
+    REAL(wp) ::  abs_dir         !< length of direction vector (for normalization)
+!    REAL(wp) ::  d_curr_target   !< rounding influence expressed as x speed component
+!    REAL(wp) ::  d_prev_target   !< rounding influence expressed as x speed component
+    REAL(wp) ::  dir_x           !< direction of agent (x)
+    REAL(wp) ::  dir_y           !< direction of agent (y)
+!    REAL(wp) ::  dist_round = 3. !< distance at which agents start rounding a corner
+    REAL(wp) ::  dtit            !< distance to intermittent target
+!    REAL(wp) ::  round_fac  = 0.2 !< factor for rounding influence
+!    REAL(wp) ::  speed_round_x   !< rounding influence expressed as x speed component
+!    REAL(wp) ::  speed_round_y   !< rounding influence expressed as x speed component
+!
+!-- Loop over all agents in the current grid box
+    DO  n = 1, number_of_agents
+       path_flag = .FALSE.
+       pc = agents(n)%path_counter
+!
+!--    If no path was calculated for agent yet, do it.
+       IF ( pc >= 999 )  THEN
+          CALL mas_nav_find_path(n)
           pc = agents(n)%path_counter
+!
+!--       If no path was calculated for agent yet, do it
+          IF ( pc >= 999 ) THEN
+!--    Check if new path must be calculated and if so, do it.
+       ELSE
+!
+!--       Case one: Agent has come close enough to intermittent target.
+!--                 -> chose new int target and calculate rest of path if no
+!--                    new intermittent targets are left
+          dtit = SQRT(   ( agents(n)%x - agents(n)%path_x(pc) )**2                                 &
+                       + ( agents(n)%y - agents(n)%path_y(pc) )**2 )
+          IF ( dtit < dist_to_int_target )  THEN
+             agents(n)%path_counter = agents(n)%path_counter + 1
+             pc = agents(n)%path_counter
+!
+!--          Path counter out of scope (each agent can store a maximum of 15 intermittent targets on
+!--          the way to its final target); new path must be calculated.
+             IF ( pc >= SIZE( agents(n)%path_x) )  THEN
+                path_flag = .TRUE.
+             ENDIF
+!
+!--          Case two: Agent too far from path
+!--                    -> set flag for new path to be calculated
+          ELSEIF ( dist_point_to_edge(agents(n)%path_x(pc-1),                                      &
+                                      agents(n)%path_y(pc-1),                                      &
+                                      agents(n)%path_x(pc),                                        &
+                                      agents(n)%path_y(pc),                                        &
+                                      agents(n)%x, agents(n)%y)                                    &
+                   > max_dist_from_path )                                                          &
+          THEN
+             path_flag = .TRUE.
+          ENDIF
+!
+!--       If one of the above two cases was true, calculate new path and reset 0th path point.
+!--       This point (the last target the agent had) is needed for the agent's rounding of corners
+!--       and the calculation of its deviation from its current path.
+          IF ( path_flag )  THEN
              CALL mas_nav_find_path(n)
              pc = agents(n)%path_counter
+!
-!--       Check if new path must be calculated and if so, do it
-          ELSE
+!
-!--          Case one: Agent has come close enough to intermittent target.
-!--                    -> chose new int target and calculate rest of path if no
-!--                       new intermittent targets are left
-             dtit = SQRT((agents(n)%x - agents(n)%path_x(pc))**2               &
-                       + (agents(n)%y - agents(n)%path_y(pc))**2)
-             IF ( dtit < dist_to_int_target ) THEN
-                agents(n)%path_counter = agents(n)%path_counter + 1
-                pc = agents(n)%path_counter
+!
-!--             Path counter out of scope (each agent can store a maximum of 15
-!--             intermittent targets on the way to her final target); new path
-!--             must be calculated
-                IF ( pc >= SIZE(agents(n)%path_x) ) THEN
-                   path_flag = .TRUE.
-                ENDIF
+!
-!--          Case two: Agent too far from path
-!--                    -> set flag for new path to be calculated
-             ELSEIF ( dist_point_to_edge(agents(n)%path_x(pc-1),               &
-                                         agents(n)%path_y(pc-1),               &
-                                         agents(n)%path_x(pc),                 &
-                                         agents(n)%path_y(pc),                 &
-                                         agents(n)%x, agents(n)%y)             &
-                      > max_dist_from_path )                                   &
-             THEN
-                path_flag = .TRUE.
-             ENDIF
+!
-!--          If either of the above two cases was true, calculate new path and
-!--          reset 0th path point. This point (the last target the agent had)
-!--          is needed for the agents rounding of corners and the calculation
-!--          of her deviation from her current path
-             IF ( path_flag ) THEN
-                CALL mas_nav_find_path(n)
-                pc = agents(n)%path_counter
-             ENDIF
           ENDIF
+!
+!--       Normalize direction vector
+          abs_dir             = 1.0d-12
+          dir_x               = agents(n)%path_x(pc) - agents(n)%x
+          dir_y               = agents(n)%path_y(pc) - agents(n)%y
+          abs_dir             = SQRT(dir_x**2 + dir_y**2)+1.0d-12
+!--         needed later for corner rounding
+!           dir_x               = dir_x/abs_dir
+!           dir_y               = dir_y/abs_dir
+!           dir_x               = dir_x + speed_round_x
+!           dir_y               = dir_y + speed_round_y
+!           abs_dir             = SQRT(dir_x**2 + dir_y**2)+1.0d-12
+          agents(n)%speed_e_x = dir_x/abs_dir
+          agents(n)%speed_e_y = dir_y/abs_dir
+       ENDDO
+       ENDIF
+!
+!--    Normalize direction vector
+       abs_dir             = 1.0d-12
+       dir_x               = agents(n)%path_x(pc) - agents(n)%x
+       dir_y               = agents(n)%path_y(pc) - agents(n)%y
+       abs_dir             = SQRT( dir_x**2 + dir_y**2 )+1.0d-12
+!--      needed later for corner rounding
+!        dir_x               = dir_x/abs_dir
+!        dir_y               = dir_y/abs_dir
+!        dir_x               = dir_x + speed_round_x
+!        dir_y               = dir_y + speed_round_y
+!        abs_dir             = SQRT(dir_x**2 + dir_y**2)+1.0d-12
+       agents(n)%speed_e_x = dir_x/abs_dir
+       agents(n)%speed_e_y = dir_y/abs_dir
+    ENDDO
+!
 …
 !           speed_round_x = 0.
 !           speed_round_y = 0.
+!
+!
 !           d_curr_target = SQRT( (agents(n)%path_x(pc) - agents(n)%x)**2 +      &
 !                                 (agents(n)%path_y(pc) - agents(n)%y)**2 )
 …
 !                              SIN( pi/dist_round*d_curr_target )
 !           ENDIF
+!
 !           IF ( d_prev_target < dist_round ) THEN
 !              IF ( agents(n)%path_x(pc) /= agents(n)%path_x(pc+1) ) THEN
+!
+!           IF ( d_prev_target < dist_round )  THEN
+!              IF ( agents(n)%path_x(pc) /= agents(n)%path_x(pc+1) )  THEN
 !                 speed_round_x = speed_round_x +                                   &
 !                                 (agents(n)%path_x(pc) - agents(n)%path_x(pc+1)) / &
 …
 !                                 SIN( pi/dist_round*d_prev_target )
 !              ENDIF
+!
 !              IF ( agents(n)%path_y(pc) /= agents(n)%path_y(pc+1) ) THEN
+!
+!              IF ( agents(n)%path_y(pc) /= agents(n)%path_y(pc+1) )  THEN
 !                 speed_round_y = speed_round_y +                                   &
 !                              (agents(n)%path_y(pc) - agents(n)%path_y(pc+1)) / &
 …
 !                              SIN( pi/dist_round*d_prev_target )
 !              ENDIF
 !           ENDIF
     END SUBROUTINE mas_agent_direction
 !------------------------------------------------------------------------------!
+ END SUBROUTINE mas_agent_direction
+!--------------------------------------------------------------------------------------------------!
 ! Description:
 ! ------------
 !> Boundary conditions for maximum time, target reached and out of domain
+!------------------------------------------------------------------------------!
+    SUBROUTINE mas_boundary_conds( location )
+       IMPLICIT NONE
+       CHARACTER (LEN=*) ::  location !< Identifier
+       INTEGER(iwp) ::  n   !< agent number
+       INTEGER(iwp) ::  grp !< agent group
+       REAL(wp) ::  dist_to_target !< distance to target
+       IF ( location == 'max_sim_time' )  THEN
+!
+!--       Delete agents that have been simulated longer than allowed
+          DO  n = 1, number_of_agents
+             IF ( agents(n)%age > agent_maximum_age  .AND.                     &
+                  agents(n)%agent_mask )                                       &
+             THEN
+                agents(n)%agent_mask  = .FALSE.
+                deleted_agents = deleted_agents + 1
+             ENDIF
+          ENDDO
+       ENDIF
+       IF ( location == 'target_area' )  THEN
+!
+!--       Delete agents that entered target region
+          DO  n = 1, number_of_agents
+             grp = agents(n)%group
+             dist_to_target = SQRT((agents(n)%x-at_x(grp))**2                  &
+                                 + (agents(n)%y-at_y(grp))**2)
+             IF ( dist_to_target < dist_target_reached ) THEN
+                agents(n)%agent_mask  = .FALSE.
+                deleted_agents = deleted_agents + 1
+             ENDIF
+          ENDDO
+       ENDIF
+    END SUBROUTINE mas_boundary_conds
+!------------------------------------------------------------------------------!
+!--------------------------------------------------------------------------------------------------!
+ SUBROUTINE mas_boundary_conds( location )
+    IMPLICIT NONE
+    CHARACTER (LEN=*) ::  location  !< Identifier
+    INTEGER(iwp) ::  grp  !< agent group
+    INTEGER(iwp) ::  n    !< agent number
+    REAL(wp) ::  dist_to_target !< distance to target
+    IF ( location == 'max_sim_time' )  THEN
+!
+!--    Delete agents that have been simulated longer than allowed
+       DO  n = 1, number_of_agents
+          IF ( agents(n)%age > agent_maximum_age  .AND.  agents(n)%agent_mask )  THEN
+             agents(n)%agent_mask  = .FALSE.
+             deleted_agents = deleted_agents + 1
+          ENDIF
+       ENDDO
+    ENDIF
+    IF ( location == 'target_area' )  THEN
+!
+!--    Delete agents that entered target region
+       DO  n = 1, number_of_agents
+          grp = agents(n)%group
+          dist_to_target = SQRT( ( agents(n)%x - at_x(grp) )**2 + ( agents(n)%y - at_y(grp) )**2 )
+          IF ( dist_to_target < dist_target_reached )  THEN
+             agents(n)%agent_mask  = .FALSE.
+             deleted_agents = deleted_agents + 1
+          ENDIF
+       ENDDO
+    ENDIF
+ END SUBROUTINE mas_boundary_conds
+!--------------------------------------------------------------------------------------------------!
 ! Description:
 ! ------------
 !> Release new agents at their respective sources
+!------------------------------------------------------------------------------!
+    SUBROUTINE mas_create_agent (phase)
+       IMPLICIT  NONE
+       INTEGER(iwp) ::  alloc_size  !< relative increase of allocated memory for agents
+       INTEGER(iwp) ::  i           !< loop variable ( agent groups )
+       INTEGER(iwp) ::  ip          !< index variable along x
+       INTEGER(iwp) ::  jp          !< index variable along y
+       INTEGER(iwp) ::  loop_stride !< loop variable for initialization
+       INTEGER(iwp) ::  n           !< loop variable ( number of agents )
+       INTEGER(iwp) ::  new_size    !< new size of allocated memory for agents
+       INTEGER(iwp) ::  rn_side     !< index of agent path
+       INTEGER(iwp), INTENT(IN) ::  phase       !< mode of inititialization
+       INTEGER(iwp), DIMENSION(nysg:nyng,nxlg:nxrg) ::  local_count !< start address of new agent
+       INTEGER(iwp), DIMENSION(nysg:nyng,nxlg:nxrg) ::  local_start !< start address of new agent
+       LOGICAL ::  first_stride !< flag for initialization
+       REAL(wp) ::  pos_x       !< increment for agent position in x
+       REAL(wp) ::  pos_y       !< increment for agent position in y
+       REAL(wp) ::  rand_contr  !< dummy argument for random position
+       REAL(wp) ::  rn_side_dum !< index of agent path
+       TYPE(agent_type),TARGET ::  tmp_agent !< temporary agent used for initialization
+!
+!--    Calculate agent positions and store agent attributes, if
+!--    agent is situated on this PE
+       DO  loop_stride = 1, 2
+          first_stride = (loop_stride == 1)
+          IF ( first_stride )   THEN
+             local_count = 0           ! count number of agents
+          ELSE
+             local_count = agt_count   ! Start address of new agents
+          ENDIF
+          DO  i = 1, number_of_agent_groups
+             pos_y = ass(i)
+             DO WHILE ( pos_y <= asn(i) )
+                IF ( pos_y >= nys * dy  .AND.                                  &
+                           pos_y <  ( nyn + 1 ) * dy  )                        &
+                THEN
+                   pos_x = asl(i)
+            xloop: DO WHILE ( pos_x <= asr(i) )
+                      IF ( pos_x >= nxl * dx  .AND.                            &
+                                 pos_x <  ( nxr + 1) * dx )                    &
+                      THEN
+                         tmp_agent%agent_mask = .TRUE.
+                         tmp_agent%group         = i
+                         tmp_agent%id            = 0_idp
+                         tmp_agent%block_nr      = -1
+                         tmp_agent%path_counter  = 999 !SIZE(tmp_agent%path_x)
+                         tmp_agent%age           = 0.0_wp
+                         tmp_agent%age_m         = 0.0_wp
+                         tmp_agent%dt_sum        = 0.0_wp
+                         tmp_agent%clo           = -999.0_wp
+                         tmp_agent%energy_storage= 0.0_wp
+                         tmp_agent%ipt           = 99999.0_wp
+                         tmp_agent%clothing_temp = -999._wp      !< energy stored by agent (W)
+                         tmp_agent%actlev        = 134.6862_wp   !< metabolic + work energy of the person
+                         tmp_agent%age_years     = 35._wp        !< physical age of the person
+                         tmp_agent%weight        = 75._wp        !< total weight of the person (kg)
+                         tmp_agent%height        = 1.75_wp       !< height of the person (m)
+                         tmp_agent%work          = 134.6862_wp   !< workload of the agent (W)
+                         tmp_agent%sex           = 1             !< agents gender: 1 = male, 2 = female
+                         tmp_agent%force_x       = 0.0_wp
+                         tmp_agent%force_y       = 0.0_wp
+                         tmp_agent%origin_x      = pos_x
+                         tmp_agent%origin_y      = pos_y
+                         tmp_agent%speed_abs     = 0.0_wp
+                         tmp_agent%speed_e_x     = 0.0_wp
+                         tmp_agent%speed_e_y     = 0.0_wp
+                         tmp_agent%speed_des     = random_normal(desired_speed,&
+                                                                 des_sp_sig)
+                         tmp_agent%speed_x       = 0.0_wp
+                         tmp_agent%speed_y       = 0.0_wp
+                         tmp_agent%x             = pos_x
+                         tmp_agent%y             = pos_y
+                         tmp_agent%path_x        = -1.0_wp
+                         tmp_agent%path_y        = -1.0_wp
+                         tmp_agent%t_x           = - pi
+                         tmp_agent%t_y           = - pi
+!
+!--                      Determine the grid indices of the agent position
+                         ip = tmp_agent%x * ddx
+                         jp = tmp_agent%y * ddy
+!
+!--                      Give each agent its target
+                         IF ( a_rand_target(i) ) THEN
+!
+!--                         Agent shall receive random target just outside
+!--                         simulated area
+                            rn_side_dum = random_function(iran_agent)
+                            rn_side     = FLOOR(4.*rn_side_dum)
+                            IF ( rn_side < 2 ) THEN
+                               IF ( rn_side == 0 ) THEN
+                                  tmp_agent%t_y = -2*dy
+                               ELSE
+                                  tmp_agent%t_y = (ny+3)*dy
+                               ENDIF
+                               tmp_agent%t_x = random_function(iran_agent) *   &
+                                               (nx+1)*dx
+!--------------------------------------------------------------------------------------------------!
+ SUBROUTINE mas_create_agent ( phase )
+    IMPLICIT  NONE
+    INTEGER(iwp) ::  alloc_size  !< relative increase of allocated memory for agents
+    INTEGER(iwp) ::  i           !< loop variable ( agent groups )
+    INTEGER(iwp) ::  ip          !< index variable along x
+    INTEGER(iwp) ::  jp          !< index variable along y
+    INTEGER(iwp) ::  loop_stride !< loop variable for initialization
+    INTEGER(iwp) ::  n           !< loop variable ( number of agents )
+    INTEGER(iwp) ::  new_size    !< new size of allocated memory for agents
+    INTEGER(iwp) ::  rn_side     !< index of agent path
+    INTEGER(iwp), INTENT(IN) ::  phase       !< mode of inititialization
+    INTEGER(iwp), DIMENSION(nysg:nyng,nxlg:nxrg) ::  local_count !< start address of new agent
+    INTEGER(iwp), DIMENSION(nysg:nyng,nxlg:nxrg) ::  local_start !< start address of new agent
+    LOGICAL ::  first_stride !< flag for initialization
+    REAL(wp) ::  pos_x       !< increment for agent position in x
+    REAL(wp) ::  pos_y       !< increment for agent position in y
+    REAL(wp) ::  rand_contr  !< dummy argument for random position
+    REAL(wp) ::  rn_side_dum !< index of agent path
+    TYPE(agent_type),TARGET ::  tmp_agent !< temporary agent used for initialization
+!
+!-- Calculate agent positions and store agent attributes, if agent is situated on this PE.
+    DO  loop_stride = 1, 2
+       first_stride = (loop_stride == 1)
+       IF ( first_stride )  THEN
+          local_count = 0           ! count number of agents
+       ELSE
+          local_count = agt_count   ! Start address of new agents
+       ENDIF
+       DO  i = 1, number_of_agent_groups
+          pos_y = ass(i)
+          DO WHILE ( pos_y <= asn(i) )
+             IF ( pos_y >= nys * dy  .AND.  pos_y <  ( nyn + 1 ) * dy  )  THEN
+                pos_x = asl(i)
+         xloop: DO WHILE ( pos_x <= asr(i) )
+                   IF ( pos_x >= nxl * dx  .AND.  pos_x <  ( nxr + 1) * dx )  THEN
+                      tmp_agent%agent_mask = .TRUE.
+                      tmp_agent%group         = i
+                      tmp_agent%id            = 0_idp
+                      tmp_agent%block_nr      = -1
+                      tmp_agent%path_counter  = 999 !SIZE(tmp_agent%path_x)
+                      tmp_agent%age           = 0.0_wp
+                      tmp_agent%age_m         = 0.0_wp
+                      tmp_agent%dt_sum        = 0.0_wp
+                      tmp_agent%clo           = -999.0_wp
+                      tmp_agent%energy_storage= 0.0_wp
+                      tmp_agent%ipt           = 99999.0_wp
+                      tmp_agent%clothing_temp = -999._wp      !< energy stored by agent (W)
+                      tmp_agent%actlev        = 134.6862_wp   !< metabolic + work energy of the person
+                      tmp_agent%age_years     = 35._wp        !< physical age of the person
+                      tmp_agent%weight        = 75._wp        !< total weight of the person (kg)
+                      tmp_agent%height        = 1.75_wp       !< height of the person (m)
+                      tmp_agent%work          = 134.6862_wp   !< workload of the agent (W)
+                      tmp_agent%sex           = 1             !< agents gender: 1 = male, 2 = female
+                      tmp_agent%force_x       = 0.0_wp
+                      tmp_agent%force_y       = 0.0_wp
+                      tmp_agent%origin_x      = pos_x
+                      tmp_agent%origin_y      = pos_y
+                      tmp_agent%speed_abs     = 0.0_wp
+                      tmp_agent%speed_e_x     = 0.0_wp
+                      tmp_agent%speed_e_y     = 0.0_wp
+                      tmp_agent%speed_des     = random_normal(desired_speed,des_sp_sig)
+                      tmp_agent%speed_x       = 0.0_wp
+                      tmp_agent%speed_y       = 0.0_wp
+                      tmp_agent%x             = pos_x
+                      tmp_agent%y             = pos_y
+                      tmp_agent%path_x        = -1.0_wp
+                      tmp_agent%path_y        = -1.0_wp
+                      tmp_agent%t_x           = - pi
+                      tmp_agent%t_y           = - pi
+!
+!--                   Determine the grid indices of the agent position
+                      ip = tmp_agent%x * ddx
+                      jp = tmp_agent%y * ddy
+!
+!--                   Give each agent its target
+                      IF ( a_rand_target(i) )  THEN
+!
+!--                      Agent shall receive random target just outside simulated area
+                         rn_side_dum = random_function(iran_agent)
+                         rn_side     = FLOOR( 4.*rn_side_dum )
+                         IF ( rn_side < 2 )  THEN
+                            IF ( rn_side == 0 )  THEN
+                               tmp_agent%t_y = -2 * dy
                             ELSE
+                               IF ( rn_side == 2 ) THEN
+                                  tmp_agent%t_x = -2*dx
+                               ELSE
+                                  tmp_agent%t_x = (nx+3)*dx
+                               ENDIF
+                               tmp_agent%t_y = random_function(iran_agent) *   &
+                                               (ny+1)*dy
+                               tmp_agent%t_y = ( ny + 3 ) * dy
                             ENDIF
+!
+!--                      Agent gets target of her group
+                            tmp_agent%t_x = random_function(iran_agent) * ( nx + 1 ) * dx
                          ELSE
+                            tmp_agent%t_x = at_x(i)
+                            tmp_agent%t_y = at_y(i)
+                            IF ( rn_side == 2 )  THEN
+                               tmp_agent%t_x = -2 * dx
+                            ELSE
+                               tmp_agent%t_x = ( nx + 3 ) * dx
+                            ENDIF
+                            tmp_agent%t_y = random_function(iran_agent) * ( ny + 1 ) * dy
                          ENDIF
+                         local_count(jp,ip) = local_count(jp,ip) + 1
+                         IF ( .NOT. first_stride )  THEN
+                            grid_agents(jp,ip)%agents(local_count(jp,ip))      &
+                                              = tmp_agent
+                         ENDIF
+!
+!--                   Agent gets target of her group
+                      ELSE
+                         tmp_agent%t_x = at_x(i)
+                         tmp_agent%t_y = at_y(i)
                       ENDIF
+                      pos_x = pos_x + adx(i)
+                   ENDDO xloop
+                ENDIF
+                pos_y = pos_y + ady(i)
+             ENDDO
+                      local_count(jp,ip) = local_count(jp,ip) + 1
+                      IF ( .NOT. first_stride )  THEN
+                         grid_agents(jp,ip)%agents(local_count(jp,ip)) = tmp_agent
+                      ENDIF
+                   ENDIF
+                   pos_x = pos_x + adx(i)
+                ENDDO xloop
+             ENDIF
+             pos_y = pos_y + ady(i)
           ENDDO
+!
+!--       Allocate or reallocate agents array to new size
+          IF ( first_stride )  THEN
+             DO  ip = nxlg, nxrg
+                DO  jp = nysg, nyng
+                   IF ( phase == PHASE_INIT )  THEN
+                      IF ( local_count(jp,ip) > 0 )  THEN
+                         alloc_size = MAX( INT( local_count(jp,ip) *           &
+                            ( 1.0_wp + alloc_factor_mas / 100.0_wp ) ),        &
+                            min_nr_agent )
+                      ELSE
+                         alloc_size = min_nr_agent
+                      ENDIF
+                      ALLOCATE(grid_agents(jp,ip)%agents(1:alloc_size))
+                      DO  n = 1, alloc_size
+                         grid_agents(jp,ip)%agents(n) = zero_agent
+                      ENDDO
+                   ELSEIF ( phase == PHASE_RELEASE )  THEN
+                      IF ( local_count(jp,ip) > 0 )  THEN
+                         new_size   = local_count(jp,ip) + agt_count(jp,ip)
+                         alloc_size = MAX( INT( new_size * ( 1.0_wp +          &
+                            alloc_factor_mas / 100.0_wp ) ), min_nr_agent )
+                         IF( alloc_size > SIZE( grid_agents(jp,ip)%agents) )   &
+                         THEN
+                            CALL mas_eh_realloc_agents_array(ip,jp,alloc_size)
+                         ENDIF
+       ENDDO
+!
+!--    Allocate or reallocate agents array to new size
+       IF ( first_stride )  THEN
+          DO  ip = nxlg, nxrg
+             DO  jp = nysg, nyng
+                IF ( phase == phase_init )  THEN
+                   IF ( local_count(jp,ip) > 0 )  THEN
+                      alloc_size = MAX( INT( local_count(jp,ip) *                                  &
+                                             ( 1.0_wp + alloc_factor_mas / 100.0_wp ) ),           &
+                                        min_nr_agent )
+                   ELSE
+                      alloc_size = min_nr_agent
+                   ENDIF
+                   ALLOCATE( grid_agents(jp,ip)%agents(1:alloc_size) )
+                   DO  n = 1, alloc_size
+                      grid_agents(jp,ip)%agents(n) = zero_agent
+                   ENDDO
+                ELSEIF ( phase == phase_release )  THEN
+                   IF ( local_count(jp,ip) > 0 )  THEN
+                      new_size   = local_count(jp,ip) + agt_count(jp,ip)
+                      alloc_size = MAX( INT( new_size *                                            &
+                                             ( 1.0_wp + alloc_factor_mas / 100.0_wp ) ),           &
+                                        min_nr_agent )
+                      IF( alloc_size > SIZE( grid_agents(jp,ip)%agents) )  THEN
+                         CALL mas_eh_realloc_agents_array(ip,jp,alloc_size)
                       ENDIF
                    ENDIF
                 ENDDO
+                ENDIF
              ENDDO
+          ENDIF
+          ENDDO
+       ENDIF
+    ENDDO
+    local_start = agt_count+1
+    agt_count   = local_count
+!
+!-- Calculate agent IDs
+    DO  ip = nxl, nxr
+       DO  jp = nys, nyn
+          number_of_agents = agt_count(jp,ip)
+          IF ( number_of_agents <= 0 )  CYCLE
+          agents => grid_agents(jp,ip)%agents(1:number_of_agents)
+          DO  n = local_start(jp,ip), number_of_agents  !only new agents
+             agents(n)%id = 10000_idp**2 * grid_agents(jp,ip)%id_counter + 10000_idp * jp + ip
+!
+!--          Count the number of agents that have been released before
+             grid_agents(jp,ip)%id_counter = grid_agents(jp,ip)%id_counter + 1
+          ENDDO
        ENDDO
+       local_start = agt_count+1
+       agt_count   = local_count
+!
+!--    Calculate agent IDs
+    ENDDO
+!
+!-- Add random fluctuation to agent positions.
+    IF ( random_start_position_agents )  THEN
        DO  ip = nxl, nxr
           DO  jp = nys, nyn
 …
              IF ( number_of_agents <= 0 )  CYCLE
              agents => grid_agents(jp,ip)%agents(1:number_of_agents)
+             DO  n = local_start(jp,ip), number_of_agents  !only new agents
+                agents(n)%id = 10000_idp**2 * grid_agents(jp,ip)%id_counter +  &
+_idp * jp + ip
+!
+!--             Count the number of agents that have been released before
+                grid_agents(jp,ip)%id_counter = grid_agents(jp,ip)%id_counter  &
+                                                + 1
+!
+!--          Move only new agents. Moreover, limit random fluctuation in order to prevent that
+!--          agents move more than one grid box, which would lead to problems concerning agent
+!--          exchange  between processors in case adx/ady are larger than dx/dy, respectively.
+             DO  n = local_start(jp,ip), number_of_agents
+                IF ( asl(agents(n)%group) /= asr(agents(n)%group) )  THEN
+                   rand_contr = ( random_function( iran_agent ) - 0.5_wp ) * adx(agents(n)%group)
+                   agents(n)%x = agents(n)%x + MERGE( rand_contr, SIGN( dx, rand_contr ),          &
+                                                      ABS( rand_contr ) < dx                       &
+                                                    )
+                ENDIF
+                IF ( ass(agents(n)%group) /= asn(agents(n)%group) )  THEN
+                   rand_contr = ( random_function( iran_agent ) - 0.5_wp ) * ady(agents(n)%group)
+                   agents(n)%y = agents(n)%y +                                                     &
+                                 MERGE( rand_contr, SIGN( dy, rand_contr ), ABS( rand_contr ) < dy )
+                ENDIF
              ENDDO
+!
+!--          Delete agents that have been simulated longer than allowed
+             CALL mas_boundary_conds( 'max_sim_time' )
+!
+!--          Delete agents that have reached target area
+             CALL mas_boundary_conds( 'target_area' )
           ENDDO
        ENDDO
+!
+!--    Add random fluctuation to agent positions.
+       IF ( random_start_position_agents )  THEN
+          DO  ip = nxl, nxr
+             DO  jp = nys, nyn
+                number_of_agents = agt_count(jp,ip)
+                IF ( number_of_agents <= 0 )  CYCLE
+                agents => grid_agents(jp,ip)%agents(1:number_of_agents)
+!
+!--             Move only new agents. Moreover, limit random fluctuation
+!--             in order to prevent that agents move more than one grid box,
+!--             which would lead to problems concerning agent exchange
+!--             between processors in case adx/ady are larger than dx/dy,
+!--             respectively.
+                DO  n = local_start(jp,ip), number_of_agents
+                   IF ( asl(agents(n)%group) /= asr(agents(n)%group) )  THEN
+                      rand_contr = ( random_function( iran_agent ) - 0.5_wp ) *&
+                                     adx(agents(n)%group)
+                      agents(n)%x = agents(n)%x +                        &
+                              MERGE( rand_contr, SIGN( dx, rand_contr ),       &
+                                     ABS( rand_contr ) < dx                    &
+                                   )
+                   ENDIF
+                   IF ( ass(agents(n)%group) /= asn(agents(n)%group) )  THEN
+                      rand_contr = ( random_function( iran_agent ) - 0.5_wp ) *&
+                                     ady(agents(n)%group)
+                      agents(n)%y = agents(n)%y +                        &
+                              MERGE( rand_contr, SIGN( dy, rand_contr ),       &
+                                     ABS( rand_contr ) < dy )
+                   ENDIF
+                ENDDO
+!
+!--             Delete agents that have been simulated longer than allowed
+                CALL mas_boundary_conds( 'max_sim_time' )
+!
+!--             Delete agents that have reached target area
+                CALL mas_boundary_conds( 'target_area' )
+             ENDDO
+          ENDDO
+!
+!--       Exchange agents between grid cells and processors
+          CALL mas_eh_move_agent
+          CALL mas_eh_exchange_horiz
+       ENDIF
+!
+!--    In case of random_start_position_agents, delete agents identified by
+!--    mas_eh_exchange_horiz and mas_boundary_conds. Then sort agents into
+!--    blocks, which is needed for a fast interpolation of the LES fields
+!--    on the agent position.
+       CALL mas_ps_sort_in_subboxes
+!
+!--    Determine the current number of agents
+       number_of_agents = 0
+!
+!--    Exchange agents between grid cells and processors
+       CALL mas_eh_move_agent
+       CALL mas_eh_exchange_horiz
+    ENDIF
+!
+!-- In case of random_start_position_agents, delete agents identified by mas_eh_exchange_horiz and
+!-- mas_boundary_conds. Then sort agents into blocks, which is needed for a fast interpolation of
+!-- the LES fields on the agent position.
+    CALL mas_ps_sort_in_subboxes
+!
+!-- Determine the current number of agents
+    number_of_agents = 0
+    DO  ip = nxl, nxr
+       DO  jp = nys, nyn
+          number_of_agents = number_of_agents + agt_count(jp,ip)
+       ENDDO
+    ENDDO
+!
+!-- Calculate the number of agents of the total domain
+#if defined( __parallel )
+    IF ( collective_wait )  CALL MPI_BARRIER( comm2d, ierr )
+    CALL MPI_ALLREDUCE( number_of_agents, total_number_of_agents, 1, MPI_INTEGER, MPI_SUM, comm2d, &
+                        ierr )
+#else
+    total_number_of_agents = number_of_agents
+#endif
+    RETURN
+ END SUBROUTINE mas_create_agent
+!--------------------------------------------------------------------------------------------------!
+! Description:
+! ------------
+!> Creates flags that indicate if a gridbox contains edges or corners. These flags are used for
+!> agents to check if obstacles are close to them.
+!--------------------------------------------------------------------------------------------------!
+ SUBROUTINE mas_create_obstacle_flags
+    USE arrays_3d,                                                                                 &
+        ONLY:  zw
+    IMPLICIT NONE
+    INTEGER(iwp) ::  il
+    INTEGER(iwp) ::  jl
+    ALLOCATE( obstacle_flags(nysg:nyng,nxlg:nxrg) )
+    obstacle_flags = 0
+    DO  il = nxlg, nxrg
+       DO  jl = nysg, nyng
+!
+!--       Exclude cyclic topography boundary
+          IF ( il < 0 .OR. il > nx .OR. jl < 0 .OR. jl > ny ) CYCLE
+!
+!--       North edge
+          IF ( jl < nyng )  THEN
+             IF ( ( top_top_s(jl,il) - top_top_s(jl+1,il) ) > 1  .AND.                             &
+                  ( zw( top_top_w(jl,il) ) - zw( top_top_w(jl+1,il) ) ) > 0.51_wp )                &
+             THEN
+                obstacle_flags(jl,il) = IBSET( obstacle_flags(jl,il), 0 )
+             ENDIF
+          ENDIF
+!
+!--       North right corner
+          IF ( jl < nyng  .AND.  il < nxrg )  THEN
+             IF ( ( top_top_s(jl,il) - top_top_s(jl+1,il)   ) > 1  .AND.                           &
+                  ( top_top_s(jl,il) - top_top_s(jl+1,il+1) ) > 1  .AND.                           &
+                  ( top_top_s(jl,il) - top_top_s(jl,il+1)   ) > 1  .AND.                           &
+                  ( zw( top_top_w(jl,il) ) - zw( top_top_w(jl+1,il+1) ) ) > 0.51_wp )              &
+             THEN
+                obstacle_flags(jl,il) = IBSET( obstacle_flags(jl,il), 1 )
+             ENDIF
+          ENDIF
+!
+!--       Right edge
+          IF ( il < nxrg )  THEN
+             IF ( ( top_top_s(jl,il) - top_top_s(jl,il+1) ) > 1  .AND.                             &
+                  ( zw( top_top_w(jl,il) ) - zw( top_top_w(jl,il+1) ) ) > 0.51_wp )                &
+             THEN
+                obstacle_flags(jl,il) = IBSET( obstacle_flags(jl,il), 2 )
+             ENDIF
+          ENDIF
+!
+!--       South right corner
+          IF ( jl > nysg  .AND.  il < nxrg )  THEN
+             IF ( ( top_top_s(jl,il) - top_top_s(jl,il+1)   ) > 1  .AND.                           &
+                  ( top_top_s(jl,il) - top_top_s(jl-1,il+1) ) > 1  .AND.                           &
+                  ( top_top_s(jl,il) - top_top_s(jl-1,il)   ) > 1  .AND.                           &
+                  ( zw(top_top_w(jl,il) ) - zw( top_top_w(jl-1,il+1) ) ) > 0.51_wp )               &
+             THEN
+                obstacle_flags(jl,il) = IBSET( obstacle_flags(jl,il), 3 )
+             ENDIF
+          ENDIF
+!
+!--       South edge
+          IF ( jl > nysg )  THEN
+             IF ( ( top_top_s(jl,il) - top_top_s(jl-1,il) ) > 1  .AND.                             &
+                  ( zw( top_top_w(jl,il) ) - zw( top_top_w(jl-1,il) ) ) > 0.51_wp )                &
+             THEN
+                obstacle_flags(jl,il) = IBSET( obstacle_flags(jl,il), 4 )
+             ENDIF
+          ENDIF
+!
+!--       South left corner
+          IF ( jl > nysg  .AND.  il > nxlg )  THEN
+             IF ( ( top_top_s(jl,il) - top_top_s(jl-1,il)   ) > 1  .AND.                           &
+                  ( top_top_s(jl,il) - top_top_s(jl-1,il-1) ) > 1  .AND.                           &
+                  ( top_top_s(jl,il) - top_top_s(jl,il-1)   ) > 1  .AND.                           &
+                  ( zw( top_top_w(jl,il) ) - zw(top_top_w(jl-1,il-1) ) ) > 0.51_wp )               &
+             THEN
+                obstacle_flags(jl,il) = IBSET( obstacle_flags(jl,il), 5 )
+             ENDIF
+          ENDIF
+!
+!--       Left edge
+          IF ( il > nxlg )  THEN
+             IF ( ( top_top_s(jl,il) - top_top_s(jl,il-1) ) > 1  .AND.                             &
+                  ( zw(top_top_w(jl,il) ) - zw(top_top_w(jl,il-1) ) ) > 0.51_wp )                  &
+             THEN
+                obstacle_flags(jl,il) = IBSET( obstacle_flags(jl,il), 6 )
+             ENDIF
+          ENDIF
+!
+!--       North left corner
+          IF ( jl < nyng  .AND.  il > nxlg )  THEN
+             IF ( ( top_top_s(jl,il) - top_top_s(jl,il-1)   ) > 1  .AND.                           &
+                  ( top_top_s(jl,il) - top_top_s(jl+1,il-1) ) > 1  .AND.                           &
+                  ( top_top_s(jl,il) - top_top_s(jl+1,il)   ) > 1  .AND.                           &
+                  ( zw( top_top_w(jl,il) ) - zw( top_top_w(jl+1,il-1) ) ) > 0.51_wp )              &
+             THEN
+                obstacle_flags(jl,il) = IBSET( obstacle_flags(jl,il), 7 )
+             ENDIF
+          ENDIF
+       ENDDO
+    ENDDO
+ END SUBROUTINE mas_create_obstacle_flags
+!--------------------------------------------------------------------------------------------------!
+! Description:
+! ------------
+!> Write agent data in netCDF format
+!--------------------------------------------------------------------------------------------------!
+ SUBROUTINE mas_data_output_agents( ftest )
+    USE control_parameters,                                                                        &
+        ONLY:  agt_time_count, biometeorology, end_time, message_string, multi_agent_system_end,   &
+               multi_agent_system_start
+    USE netcdf_interface,                                                                          &
+        ONLY:  nc_stat, id_set_agt, id_var_time_agt, id_var_agt, netcdf_handle_error
+    USE pegrid
+#if defined( __netcdf )
+    USE NETCDF
+#endif
+    USE mas_global_attributes,                                                                     &
+        ONLY:  dim_size_agtnum
+    IMPLICIT NONE
+#if defined( __parallel )
+    INTEGER(iwp) ::  agt_size !< Agent size in bytes
+    INTEGER(iwp) ::  n        !< counter (number of PEs)
+    INTEGER(iwp) ::  noa_rcv  !< received number of agents
+#endif
+    INTEGER(iwp) ::  dummy    !< dummy
+    INTEGER(iwp) ::  ii       !< counter (x)
+    INTEGER(iwp) ::  ip       !< counter (x)
+    INTEGER(iwp) ::  jp       !< counter (y)
+    INTEGER(iwp) ::  noa      !< number of agents
+    INTEGER(iwp) ::  out_noa  !< number of agents for output
+#if defined( __parallel )
+    INTEGER(iwp), DIMENSION(0:numprocs-1) ::  noa_arr !< number of agents on each PE
+#endif
+!
+!-- SAVE attribute required to avoid compiler warning about pointer outlive the pointer target
+    TYPE(agent_type), DIMENSION(:), ALLOCATABLE, TARGET, SAVE ::  trf_agents !< all agents on current PE
+#if defined( __parallel )
+    TYPE(agent_type), DIMENSION(:), ALLOCATABLE, TARGET, SAVE ::  out_agents !< all agents in entire domain
+#endif
+    LOGICAL, INTENT (INOUT) :: ftest
+    LOGICAL, SAVE :: agt_dimension_exceeded = .FALSE.
+    CALL cpu_log( log_point_s(17), 'mas_data_output', 'start' )
+!
+!-- Get total number of agents and put all agents on one PE in one array
+    noa = 0
+    DO  ip = nxl, nxr
+       DO  jp = nys, nyn
+          noa  = noa  + agt_count(jp,ip)
+       ENDDO
+    ENDDO
+    IF ( noa > 0 )  THEN
+       ALLOCATE( trf_agents(1:noa) )
+       dummy = 1
        DO  ip = nxl, nxr
           DO  jp = nys, nyn
+             number_of_agents = number_of_agents + agt_count(jp,ip)
+             IF ( agt_count(jp,ip) == 0 )  CYCLE
+             agents => grid_agents(jp,ip)%agents(1:agt_count(jp,ip))
+             trf_agents(dummy:(dummy-1+agt_count(jp,ip))) = agents
+             dummy = dummy + agt_count(jp,ip)
           ENDDO
        ENDDO
+!
+!--    Calculate the number of agents of the total domain
+    ENDIF
 #if defined( __parallel )
+       IF ( collective_wait )  CALL MPI_BARRIER( comm2d, ierr )
+       CALL MPI_ALLREDUCE( number_of_agents, total_number_of_agents, 1, &
+       MPI_INTEGER, MPI_SUM, comm2d, ierr )
+!
+!-- Gather all agents on PE0 for output
+    IF ( myid == 0 )  THEN
+       noa_arr(0) = noa
+!
+!--    Receive data from all other PEs.
+       DO  n = 1, numprocs-1
+           CALL MPI_RECV( noa_arr(n), 1, MPI_INTEGER, n, 0, comm2d, status, ierr )
+       ENDDO
+    ELSE
+       CALL MPI_SEND( noa, 1, MPI_INTEGER, 0, 0, comm2d, ierr )
+    ENDIF
+    CALL MPI_BARRIER( comm2d, ierr )
+    agt_size = STORAGE_SIZE( zero_agent ) / 8
+    IF ( myid == 0 )  THEN
+!
+!--    Receive data from all other PEs.
+       out_noa = SUM( noa_arr )
+       IF ( out_noa > 0 )  THEN
+          ALLOCATE( out_agents(1:out_noa) )
+          IF ( noa > 0 )  THEN
+             out_agents(1:noa) = trf_agents
+          ENDIF
+          noa_rcv = noa
+          DO  n = 1, numprocs-1
+             IF ( noa_arr(n) > 0 )  THEN
+                CALL MPI_RECV( out_agents(noa_rcv+1), noa_arr(n) * agt_size, MPI_BYTE, n, 0,       &
+                               comm2d, status, ierr )
+                noa_rcv = noa_rcv + noa_arr(n)
+             ENDIF
+          ENDDO
+       ELSE
+          ALLOCATE( out_agents(1:2) )
+          out_agents = zero_agent
+          out_noa    = 2
+       ENDIF
+    ELSE
+       IF ( noa > 0 )  THEN
+          CALL MPI_SEND( trf_agents(1), noa*agt_size, MPI_BYTE, 0, 0, comm2d, ierr )
+       ENDIF
+    ENDIF
+!
+!-- A barrier has to be set, because otherwise some PEs may proceed too fast so that PE0 may receive
+!-- wrong data on tag 0.
+    CALL MPI_BARRIER( comm2d, ierr )
+#endif
+    IF ( myid == 0 )  THEN
+#if defined( __parallel )
+       agents => out_agents
 #else
        total_number_of_agents = number_of_agents
+       agents => trf_agents
 #endif
+       RETURN
+    END SUBROUTINE mas_create_agent
+!------------------------------------------------------------------------------!
+#if defined( __netcdf )
+!
+!--    Update maximum number of agents
+       maximum_number_of_agents = MAX(maximum_number_of_agents, out_noa)
+!
+!--       Output in netCDF format
+       IF ( ftest )  THEN
+!
+!--          First, define size of agent number dimension from amount of agents released, release
+!--          interval, time of agent simulation and max age of agents.
+          dim_size_agtnum = MIN( MIN( multi_agent_system_end, end_time )                           &
+                                    - multi_agent_system_start,                                    &
+                                 agent_maximum_age)
+          DO ii = 1, number_of_agent_groups
+             dim_size_agtnum = dim_size_agtnum                                                     &
+                                + ( FLOOR( ( asr(ii)-asl(ii) ) / adx(ii) ) + 1 )                   &
+                                * ( FLOOR( ( asn(ii)-ass(ii) ) / ady(ii) ) + 1 )                   &
+                                * ( FLOOR( dim_size_agtnum / dt_arel )     + 1 )                   &
+                                * dim_size_factor_agtnum
+             dim_size_agtnum = MIN( dim_size_agtnum, dim_size_agtnum_manual )
+          ENDDO
+          CALL check_open( 118 )
+       ENDIF
+!
+!--    Update the NetCDF time axis
+       agt_time_count = agt_time_count + 1
+       IF ( .NOT. agt_dimension_exceeded )  THEN
+!
+!--       If number of agents to be output exceeds dimension, set flag and print warning.
+          IF ( out_noa > dim_size_agtnum )  THEN
+             agt_dimension_exceeded = .TRUE.
+             WRITE( message_string, '(A,F11.1,2(A,I8))' )                                          &
+                                                  'Number of agents exceeds agent dimension.' //   &
+                                                  '&Starting at time_since_reference_point = ',    &
+                                                  time_since_reference_point,                      &
+                                                  ' s, &data may be missing.'//                    &
+                                                  '&Number of agents:     ', out_noa,              &
+                                                  '&Agent dimension size: ', dim_size_agtnum
+             CALL message( 'mas_data_output_agents', 'PA0420', 0, 1, 0, 6, 0 )
+          ENDIF
+       ENDIF
+!
+!--    Reduce number of output agents to dimension size, if necessary.
+       IF ( agt_dimension_exceeded )  THEN
+          out_noa = MIN( out_noa, dim_size_agtnum )
+       ENDIF
+       nc_stat = NF90_PUT_VAR( id_set_agt, id_var_time_agt,                                        &
+                               (/ time_since_reference_point + agent_substep_time /),              &
+                               start = (/ agt_time_count /),                                       &
+                               count = (/ 1 /) )
+       CALL netcdf_handle_error( 'mas_data_output_agents', 1 )
+!
+!--       Output agent attributes
+       nc_stat = NF90_PUT_VAR( id_set_agt, id_var_agt(1), agents%id,                               &
+                               start = (/ 1, agt_time_count /),                                    &
+                               count = (/ out_noa /) )
+       CALL netcdf_handle_error( 'mas_data_output_agents', 2 )
+       nc_stat = NF90_PUT_VAR( id_set_agt, id_var_agt(2), agents%x,                                &
+                               start = (/ 1, agt_time_count /),                                    &
+                               count = (/ out_noa /) )
+       CALL netcdf_handle_error( 'mas_data_output_agents', 3 )
+       nc_stat = NF90_PUT_VAR( id_set_agt, id_var_agt(3), agents%y,                                &
+                               start = (/ 1, agt_time_count /),                                    &
+                               count = (/ out_noa /) )
+       CALL netcdf_handle_error( 'mas_data_output_agents', 4 )
+       nc_stat = NF90_PUT_VAR( id_set_agt, id_var_agt(4), agents%windspeed,                        &
+                               start = (/ 1, agt_time_count /),                                    &
+                               count = (/ out_noa /) )
+       CALL netcdf_handle_error( 'mas_data_output_agents', 5 )
+       nc_stat = NF90_PUT_VAR( id_set_agt, id_var_agt(5), agents%t,                                &
+                               start = (/ 1, agt_time_count /),                                    &
+                               count = (/ out_noa /) )
+       CALL netcdf_handle_error( 'mas_data_output_agents', 6 )
+       nc_stat = NF90_PUT_VAR( id_set_agt, id_var_agt(6), agents%group,                            &
+                               start = (/ 1, agt_time_count /),                                    &
+                               count = (/ out_noa /) )
+       CALL netcdf_handle_error( 'mas_data_output_agents', 7 )
+       IF ( biometeorology )  THEN
+          nc_stat = NF90_PUT_VAR( id_set_agt, id_var_agt(7), agents%ipt,                           &
+                                  start = (/ 1, agt_time_count /),                                 &
+                                  count = (/ out_noa /) )
+          CALL netcdf_handle_error( 'mas_data_output_agents', 8 )
+       ENDIF
+!           nc_stat = NF90_PUT_VAR( id_set_agt, id_var_agt(8), agents%pm10,                         &
+!                                   start = (/ 1, agt_time_count /),                                &
+!                                   count = (/ out_noa /) )
+!           CALL netcdf_handle_error( 'mas_data_output_agents', 9 )
+!
+!           nc_stat = NF90_PUT_VAR( id_set_agt, id_var_agt(9), agents%pm25,                         &
+!                                   start = (/ 1, agt_time_count /),                                &
+!                                   count = (/ out_noa /) )
+!           CALL netcdf_handle_error( 'mas_data_output_agents', 10 )
+!
+!
+!           nc_stat = NF90_PUT_VAR( id_set_agt, id_var_agt(9), agents%uv,                           &
+!                                   start = (/ 1, agt_time_count /),                                &
+!                                   count = (/ out_noa /) )
+!           CALL netcdf_handle_error( 'mas_data_output_agents', 10 )
+       CALL cpu_log( log_point_s(17), 'mas_data_output', 'stop' )
+#endif
+#if defined( __parallel )
+       IF ( ALLOCATED( out_agents ) ) DEALLOCATE( out_agents )
+#endif
+    ELSE
+       CALL cpu_log( log_point_s(17), 'mas_data_output', 'stop' )
+    ENDIF
+    IF ( ALLOCATED( trf_agents ) ) DEALLOCATE( trf_agents )
+ END SUBROUTINE mas_data_output_agents
+#if defined( __parallel )
+!--------------------------------------------------------------------------------------------------!
 ! Description:
 ! ------------
+!> Creates flags that indicate if a gridbox contains edges or corners. These
+!> flags are used for agents to check if obstacles are close to them.
+!------------------------------------------------------------------------------!
+    SUBROUTINE mas_create_obstacle_flags
+       USE arrays_3d,                                                          &
+           ONLY:  zw
+       IMPLICIT NONE
+       INTEGER(iwp) ::  il
+       INTEGER(iwp) ::  jl
+       ALLOCATE(obstacle_flags(nysg:nyng,nxlg:nxrg))
+       obstacle_flags = 0
+       DO il = nxlg, nxrg
+          DO jl = nysg, nyng
+!
+!--          Exclude cyclic topography boundary
+             IF ( il < 0 .OR. il > nx .OR. jl < 0 .OR. jl > ny ) CYCLE
+!
+!--          North edge
+             IF ( jl < nyng ) THEN
+                IF ( ( top_top_s(jl,il) - top_top_s(jl+1,il) ) > 1 .AND.       &
+                     ( zw( top_top_w(jl,il) ) -                                &
+                       zw( top_top_w(jl+1,il) ) ) > .51_wp )                   &
+                THEN
+                   obstacle_flags(jl,il) = IBSET( obstacle_flags(jl,il), 0 )
+!> If an agent moves from one processor to another, this subroutine moves the corresponding elements
+!> from the agent arrays of the old grid cells to the agent arrays of the new grid cells.
+!--------------------------------------------------------------------------------------------------!
+ SUBROUTINE mas_eh_add_agents_to_gridcell (agent_array)
+    IMPLICIT NONE
+    INTEGER(iwp) ::  aindex  !< dummy argument for new number of agents per grid box
+    INTEGER(iwp) ::  ip      !< grid index (x) of agent
+    INTEGER(iwp) ::  jp      !< grid index (x) of agent
+    INTEGER(iwp) ::  n       !< index variable of agent
+    LOGICAL ::  pack_done  !< flag to indicate that packing is done
+    TYPE(agent_type), DIMENSION(:), INTENT(IN)  ::  agent_array  !< new agents in a grid box
+    TYPE(agent_type), DIMENSION(:), ALLOCATABLE ::  temp_ns      !< temporary agent array for reallocation
+    pack_done     = .FALSE.
+    DO  n = 1, SIZE(agent_array)
+       IF ( .NOT. agent_array(n)%agent_mask )  CYCLE
+       ip = agent_array(n)%x * ddx
+       jp = agent_array(n)%y * ddy
+       IF ( ip >= nxl  .AND.  ip <= nxr  .AND.  jp >= nys  .AND.  jp <= nyn )  THEN ! agent stays on processor
+          number_of_agents = agt_count(jp,ip)
+          agents => grid_agents(jp,ip)%agents(1:number_of_agents)
+          aindex = agt_count(jp,ip)+1
+          IF( aindex > SIZE( grid_agents(jp,ip)%agents ) )  THEN
+             IF ( pack_done )  THEN
+                CALL mas_eh_realloc_agents_array (ip,jp)
+             ELSE
+                CALL mas_ps_pack
+                agt_count(jp,ip) = number_of_agents
+                aindex = agt_count(jp,ip)+1
+                IF ( aindex > SIZE( grid_agents(jp,ip)%agents ) )  THEN
+                   CALL mas_eh_realloc_agents_array (ip,jp)
+                ENDIF
+                pack_done = .TRUE.
+             ENDIF
+          ENDIF
+          grid_agents(jp,ip)%agents(aindex) = agent_array(n)
+          agt_count(jp,ip) = aindex
+       ELSE
+          IF ( jp <= nys - 1 )  THEN
+             nr_move_south = nr_move_south+1
+!
+!--          Before agent information is swapped to exchange-array, check if enough memory is
+!--          allocated. If required, reallocate exchange array.
+             IF ( nr_move_south > SIZE( move_also_south ) )  THEN
+!
+!--             At first, allocate further temporary array to swap agent information.
+                ALLOCATE( temp_ns( SIZE( move_also_south ) + nr_2_direction_move ) )
+                temp_ns(1:nr_move_south-1) = move_also_south(1:nr_move_south-1)
+                DEALLOCATE( move_also_south )
+                ALLOCATE( move_also_south( SIZE(temp_ns) ) )
+                move_also_south(1:nr_move_south-1) = temp_ns(1:nr_move_south-1)
+                DEALLOCATE( temp_ns )
+             ENDIF
+             move_also_south(nr_move_south) = agent_array(n)
+             IF ( jp == -1 )  THEN
+!
+!--             Apply boundary condition along y
+                IF ( ibc_mas_ns == 0 )  THEN
+                   move_also_south(nr_move_south)%y = move_also_south(nr_move_south)%y             &
+                                                      + ( ny + 1 ) * dy
+                   move_also_south(nr_move_south)%origin_y =                                       &
+                                                         move_also_south(nr_move_south)%origin_y   &
+                                                         + ( ny + 1 ) * dy
+                ELSEIF ( ibc_mas_ns == 1 )  THEN
+!
+!--                Agent absorption
+                   move_also_south(nr_move_south)%agent_mask = .FALSE.
+                   deleted_agents = deleted_agents + 1
                 ENDIF
              ENDIF
+!
+!--          North right corner
+             IF ( jl < nyng .AND. il < nxrg ) THEN
+                IF ( ( top_top_s(jl,il) - top_top_s(jl+1,il) )   > 1 .AND.     &
+                     ( top_top_s(jl,il) - top_top_s(jl+1,il+1) ) > 1 .AND.     &
+                     ( top_top_s(jl,il) - top_top_s(jl,il+1) )   > 1 .AND.     &
+                     ( zw( top_top_w(jl,il) ) -                                &
+                       zw( top_top_w(jl+1,il+1) ) ) > .51_wp )                 &
+                THEN
+                   obstacle_flags(jl,il) = IBSET( obstacle_flags(jl,il), 1 )
+                ENDIF
+          ELSEIF ( jp >= nyn+1 )  THEN
+             nr_move_north = nr_move_north+1
+!
+!--          Before agent information is swapped to exchange-array, check  if enough memory is
+!--          allocated. If required, reallocate exchange array.
+             IF ( nr_move_north > SIZE( move_also_north ) )  THEN
+!
+!--             At first, allocate further temporary array to swap agent information.
+                ALLOCATE( temp_ns( SIZE( move_also_north ) + nr_2_direction_move ) )
+                temp_ns(1:nr_move_north-1) = move_also_south(1:nr_move_north-1)
+                DEALLOCATE( move_also_north )
+                ALLOCATE( move_also_north(SIZE(temp_ns)) )
+                move_also_north(1:nr_move_north-1) = temp_ns(1:nr_move_north-1)
+                DEALLOCATE( temp_ns )
              ENDIF
+!
+!--          Right edge
+             IF ( il < nxrg ) THEN
+                IF ( ( top_top_s(jl,il) - top_top_s(jl,il+1) ) > 1 .AND.       &
+                     ( zw( top_top_w(jl,il) ) -                                &
+                       zw( top_top_w(jl,il+1) ) ) > .51_wp )                   &
+                THEN
+                   obstacle_flags(jl,il) = IBSET( obstacle_flags(jl,il), 2 )
+                ENDIF
+             ENDIF
+!
+!--          South right corner
+             IF ( jl > nysg .AND. il < nxrg ) THEN
+                IF ( ( top_top_s(jl,il) - top_top_s(jl,il+1) )   > 1 .AND.     &
+                     ( top_top_s(jl,il) - top_top_s(jl-1,il+1) ) > 1 .AND.     &
+                     ( top_top_s(jl,il) - top_top_s(jl-1,il) )   > 1 .AND.     &
+                     ( zw(top_top_w(jl,il)) -                                  &
+                       zw( top_top_w(jl-1,il+1) ) ) > .51_wp )                 &
+                THEN
+                   obstacle_flags(jl,il) = IBSET( obstacle_flags(jl,il), 3 )
+                ENDIF
+             ENDIF
+!
+!--          South edge
+             IF ( jl > nysg ) THEN
+                IF ( ( top_top_s(jl,il) - top_top_s(jl-1,il) ) > 1 .AND.       &
+                     ( zw( top_top_w(jl,il) ) -                                &
+                       zw( top_top_w(jl-1,il) ) ) > .51_wp )                   &
+                THEN
+                   obstacle_flags(jl,il) = IBSET( obstacle_flags(jl,il), 4 )
+                ENDIF
+             ENDIF
+!
+!--          South left corner
+             IF ( jl > nysg .AND. il > nxlg ) THEN
+                IF ( ( top_top_s(jl,il) - top_top_s(jl-1,il) )   > 1 .AND.     &
+                     ( top_top_s(jl,il) - top_top_s(jl-1,il-1) ) > 1 .AND.     &
+                     ( top_top_s(jl,il) - top_top_s(jl,il-1) )   > 1 .AND.     &
+                     ( zw( top_top_w(jl,il) ) -                                &
+                       zw(top_top_w(jl-1,il-1) ) ) > .51_wp )                  &
+                THEN
+                   obstacle_flags(jl,il) = IBSET( obstacle_flags(jl,il), 5 )
+                ENDIF
+             ENDIF
+!
+!--          Left edge
+             IF ( il > nxlg ) THEN
+                IF ( ( top_top_s(jl,il) - top_top_s(jl,il-1) ) > 1 .AND.       &
+                     ( zw(top_top_w(jl,il) ) -                                 &
+                       zw(top_top_w(jl,il-1) ) ) > .51_wp )                 &
+                THEN
+                   obstacle_flags(jl,il) = IBSET( obstacle_flags(jl,il), 6 )
+                ENDIF
+             ENDIF
+!
+!--          North left corner
+             IF ( jl < nyng .AND. il > nxlg ) THEN
+                IF ( ( top_top_s(jl,il) - top_top_s(jl,il-1) )   > 1 .AND.     &
+                     ( top_top_s(jl,il) - top_top_s(jl+1,il-1) ) > 1 .AND.     &
+                     ( top_top_s(jl,il) - top_top_s(jl+1,il) )   > 1 .AND.     &
+                     ( zw( top_top_w(jl,il) ) -                                &
+                       zw( top_top_w(jl+1,il-1) ) ) > .51_wp )                 &
+                THEN
+                   obstacle_flags(jl,il) = IBSET( obstacle_flags(jl,il), 7 )
+                ENDIF
+             ENDIF
+          ENDDO
+       ENDDO
+    END SUBROUTINE mas_create_obstacle_flags
+!------------------------------------------------------------------------------!
+! Description:
+! ------------
+!> Write agent data in netCDF format
+!------------------------------------------------------------------------------!
+    SUBROUTINE mas_data_output_agents( ftest )
+       USE control_parameters,                                                 &
+           ONLY:  agt_time_count, biometeorology, end_time, message_string,    &
+                  multi_agent_system_end, multi_agent_system_start
+       USE netcdf_interface,                                                   &
+           ONLY:  nc_stat, id_set_agt, id_var_time_agt,        &
+                  id_var_agt, netcdf_handle_error
+       USE pegrid
+#if defined( __netcdf )
+       USE NETCDF
+#endif
+       USE mas_global_attributes,                                              &
+           ONLY:  dim_size_agtnum
+       IMPLICIT NONE
+#if defined( __parallel )
+       INTEGER(iwp) ::  agt_size !< Agent size in bytes
+       INTEGER(iwp) ::  n        !< counter (number of PEs)
+       INTEGER(iwp) ::  noa_rcv  !< received number of agents
+#endif
+       INTEGER(iwp) ::  dummy    !< dummy
+       INTEGER(iwp) ::  ii       !< counter (x)
+       INTEGER(iwp) ::  ip       !< counter (x)
+       INTEGER(iwp) ::  jp       !< counter (y)
+       INTEGER(iwp) ::  noa      !< number of agents
+       INTEGER(iwp) ::  out_noa  !< number of agents for output
+#if defined( __parallel )
+       INTEGER(iwp), DIMENSION(0:numprocs-1) ::  noa_arr !< number of agents on each PE
+#endif
+!
+!--    SAVE attribute required to avoid compiler warning about pointer outlive the pointer target
+       TYPE(agent_type), DIMENSION(:), ALLOCATABLE, TARGET, SAVE ::  trf_agents !< all agents on current PE
+#if defined( __parallel )
+       TYPE(agent_type), DIMENSION(:), ALLOCATABLE, TARGET, SAVE ::  out_agents !< all agents in entire domain
+#endif
+       LOGICAL, INTENT (INOUT) :: ftest
+       LOGICAL, SAVE :: agt_dimension_exceeded = .FALSE.
+       CALL cpu_log( log_point_s(17), 'mas_data_output', 'start' )
+!
+!--    Get total number of agents and put all agents on one PE in one array
+       noa = 0
+       DO  ip = nxl, nxr
+          DO  jp = nys, nyn
+             noa  = noa  + agt_count(jp,ip)
+          ENDDO
+       ENDDO
+       IF(noa > 0) THEN
+          ALLOCATE(trf_agents(1:noa))
+          dummy = 1
+          DO  ip = nxl, nxr
+             DO  jp = nys, nyn
+                IF ( agt_count(jp,ip) == 0 ) CYCLE
+                agents => grid_agents(jp,ip)%agents(1:agt_count(jp,ip))
+                trf_agents(dummy:(dummy-1+agt_count(jp,ip))) = agents
+                dummy = dummy + agt_count(jp,ip)
+             ENDDO
+          ENDDO
+       ENDIF
+#if defined( __parallel )
+!
+!--    Gather all agents on PE0 for output
+       IF ( myid == 0 )  THEN
+          noa_arr(0) = noa
+!
+!--       Receive data from all other PEs.
+          DO  n = 1, numprocs-1
+              CALL MPI_RECV( noa_arr(n), 1, MPI_INTEGER,                       &
+                              n, 0, comm2d, status, ierr )
+          ENDDO
+       ELSE
+          CALL MPI_SEND( noa, 1, MPI_INTEGER, 0, 0, comm2d, ierr )
+       ENDIF
+       CALL MPI_BARRIER( comm2d, ierr )
+       agt_size = STORAGE_SIZE(zero_agent)/8
+       IF ( myid == 0 )  THEN
+!
+!--       Receive data from all other PEs.
+          out_noa = SUM(noa_arr)
+          IF ( out_noa > 0 ) THEN
+             ALLOCATE( out_agents(1:out_noa) )
+             IF ( noa > 0 ) THEN
+                out_agents(1:noa) = trf_agents
+             ENDIF
+             noa_rcv = noa
+             DO n = 1, numprocs-1
+                IF ( noa_arr(n) > 0 ) THEN
+                   CALL MPI_RECV( out_agents(noa_rcv+1), noa_arr(n)*agt_size,  &
+                                  MPI_BYTE, n, 0, comm2d, status, ierr )
+                   noa_rcv = noa_rcv + noa_arr(n)
+                ENDIF
+             ENDDO
+          ELSE
+             ALLOCATE( out_agents(1:2) )
+             out_agents = zero_agent
+             out_noa    = 2
+          ENDIF
+       ELSE
+          IF ( noa > 0 ) THEN
+             CALL MPI_SEND( trf_agents(1), noa*agt_size, MPI_BYTE, 0, 0,       &
+                                        comm2d, ierr )
+          ENDIF
+       ENDIF
+!
+!--    A barrier has to be set, because otherwise some PEs may
+!--    proceed too fast so that PE0 may receive wrong data on
+!--    tag 0
+       CALL MPI_BARRIER( comm2d, ierr )
+#endif
+       IF ( myid == 0 ) THEN
+#if defined( __parallel )
+          agents => out_agents
+#else
+          agents => trf_agents
+#endif
+#if defined( __netcdf )
+!
+!--       Update maximum number of agents
+          maximum_number_of_agents = MAX(maximum_number_of_agents, out_noa)
+!
+!--       Output in netCDF format
+          IF ( ftest ) THEN
+!
+!--          First, define size of agent number dimension from amount of agents
+!--          released, release interval, time of agent simulation and max
+!--          age of agents
+             dim_size_agtnum = MIN( MIN( multi_agent_system_end, end_time )    &
+                                       - multi_agent_system_start,             &
+                                    agent_maximum_age)
+             DO ii = 1, number_of_agent_groups
+                dim_size_agtnum = dim_size_agtnum                              &
+                                + (FLOOR( ( asr(ii)-asl(ii) ) / adx(ii) ) + 1) &
+                                * (FLOOR( ( asn(ii)-ass(ii) ) / ady(ii) ) + 1) &
+                                * (FLOOR( dim_size_agtnum / dt_arel )     + 1) &
+                                * dim_size_factor_agtnum
+                dim_size_agtnum = MIN( dim_size_agtnum, dim_size_agtnum_manual )
+             ENDDO
+             CALL check_open( 118 )
+          ENDIF
+!
+!--       Update the NetCDF time axis
+          agt_time_count = agt_time_count + 1
+          IF ( .NOT. agt_dimension_exceeded ) THEN
+!
+!--          if number of agents to be output exceeds dimension, set flag and
+!--          print warning
+             IF ( out_noa > dim_size_agtnum ) THEN
+                agt_dimension_exceeded = .TRUE.
+                WRITE(message_string,'(A,F11.1,2(A,I8))')                      &
+                                'Number of agents exceeds agent dimension.' // &
+                                '&Starting at time_since_reference_point = ',  &
+                                time_since_reference_point,                    &
+                                ' s, &data may be missing.'//                  &
+                                '&Number of agents:     ', out_noa,            &
+                                '&Agent dimension size: ', dim_size_agtnum
+                CALL message( 'mas_data_output_agents',                        &
+                              'PA0420', 0, 1, 0, 6, 0 )
+             ENDIF
+          ENDIF
+!
+!--       reduce number of output agents to dimension size, if necessary
+          IF ( agt_dimension_exceeded ) THEN
+             out_noa = MIN( out_noa, dim_size_agtnum )
+          ENDIF
+          nc_stat = NF90_PUT_VAR( id_set_agt, id_var_time_agt,                 &
+                                  (/ time_since_reference_point + agent_substep_time /),            &
+                                  start = (/ agt_time_count /),                &
+                                  count = (/ 1 /) )
+          CALL netcdf_handle_error( 'mas_data_output_agents', 1 )
+!
+!--       Output agent attributes
+          nc_stat = NF90_PUT_VAR( id_set_agt, id_var_agt(1), agents%id,        &
+                                  start = (/ 1, agt_time_count /),             &
+                                  count = (/ out_noa /) )
+          CALL netcdf_handle_error( 'mas_data_output_agents', 2 )
+          nc_stat = NF90_PUT_VAR( id_set_agt, id_var_agt(2), agents%x,         &
+                                  start = (/ 1, agt_time_count /),             &
+                                  count = (/ out_noa /) )
+          CALL netcdf_handle_error( 'mas_data_output_agents', 3 )
+          nc_stat = NF90_PUT_VAR( id_set_agt, id_var_agt(3), agents%y,         &
+                                  start = (/ 1, agt_time_count /),             &
+                                  count = (/ out_noa /) )
+          CALL netcdf_handle_error( 'mas_data_output_agents', 4 )
+          nc_stat = NF90_PUT_VAR( id_set_agt, id_var_agt(4), agents%windspeed, &
+                                  start = (/ 1, agt_time_count /),             &
+                                  count = (/ out_noa /) )
+          CALL netcdf_handle_error( 'mas_data_output_agents', 5 )
+          nc_stat = NF90_PUT_VAR( id_set_agt, id_var_agt(5), agents%t,         &
+                                  start = (/ 1, agt_time_count /),             &
+                                  count = (/ out_noa /) )
+          CALL netcdf_handle_error( 'mas_data_output_agents', 6 )
+          nc_stat = NF90_PUT_VAR( id_set_agt, id_var_agt(6), agents%group,     &
+                                  start = (/ 1, agt_time_count /),             &
+                                  count = (/ out_noa /) )
+          CALL netcdf_handle_error( 'mas_data_output_agents', 7 )
+          IF ( biometeorology )  THEN
+             nc_stat = NF90_PUT_VAR( id_set_agt, id_var_agt(7), agents%ipt,    &
+                                     start = (/ 1, agt_time_count /),          &
+                                     count = (/ out_noa /) )
+             CALL netcdf_handle_error( 'mas_data_output_agents', 8 )
+          ENDIF
+!           nc_stat = NF90_PUT_VAR( id_set_agt, id_var_agt(8), agents%pm10,      &
+!                                   start = (/ 1, agt_time_count /),             &
+!                                   count = (/ out_noa /) )
+!           CALL netcdf_handle_error( 'mas_data_output_agents', 9 )
+!
+!           nc_stat = NF90_PUT_VAR( id_set_agt, id_var_agt(9), agents%pm25,      &
+!                                   start = (/ 1, agt_time_count /),             &
+!                                   count = (/ out_noa /) )
+!           CALL netcdf_handle_error( 'mas_data_output_agents', 10 )
+!
+!
+!           nc_stat = NF90_PUT_VAR( id_set_agt, id_var_agt(9), agents%uv,        &
+!                                   start = (/ 1, agt_time_count /),             &
+!                                   count = (/ out_noa /) )
+!           CALL netcdf_handle_error( 'mas_data_output_agents', 10 )
+          CALL cpu_log( log_point_s(17), 'mas_data_output', 'stop' )
+#endif
+#if defined( __parallel )
+          IF ( ALLOCATED( out_agents ) ) DEALLOCATE( out_agents )
+#endif
+       ELSE
+          CALL cpu_log( log_point_s(17), 'mas_data_output', 'stop' )
+       ENDIF
+       IF ( ALLOCATED( trf_agents ) ) DEALLOCATE( trf_agents )
+    END SUBROUTINE mas_data_output_agents
+#if defined( __parallel )
+!------------------------------------------------------------------------------!
+! Description:
+! ------------
+!> If an agent moves from one processor to another, this subroutine moves
+!> the corresponding elements from the agent arrays of the old grid cells
+!> to the agent arrays of the new grid cells.
+!------------------------------------------------------------------------------!
+    SUBROUTINE mas_eh_add_agents_to_gridcell (agent_array)
+       IMPLICIT NONE
+       INTEGER(iwp) ::  aindex !< dummy argument for new number of agents per grid box
+       INTEGER(iwp) ::  ip     !< grid index (x) of agent
+       INTEGER(iwp) ::  jp     !< grid index (x) of agent
+       INTEGER(iwp) ::  n      !< index variable of agent
+       LOGICAL ::  pack_done !< flag to indicate that packing is done
+       TYPE(agent_type), DIMENSION(:), INTENT(IN)  ::  agent_array !< new agents in a grid box
+       TYPE(agent_type), DIMENSION(:), ALLOCATABLE ::  temp_ns     !< temporary agent array for reallocation
+       pack_done     = .FALSE.
+       DO n = 1, SIZE(agent_array)
+          IF ( .NOT. agent_array(n)%agent_mask )  CYCLE
+          ip = agent_array(n)%x * ddx
+          jp = agent_array(n)%y * ddy
+          IF ( ip >= nxl  .AND.  ip <= nxr  .AND.                              &
+               jp >= nys  .AND.  jp <= nyn )  &
+          THEN ! agent stays on processor
+             number_of_agents = agt_count(jp,ip)
+             agents => grid_agents(jp,ip)%agents(1:number_of_agents)
+             aindex = agt_count(jp,ip)+1
+             IF( aindex > SIZE(grid_agents(jp,ip)%agents) )  THEN
+                IF ( pack_done )  THEN
+                   CALL mas_eh_realloc_agents_array (ip,jp)
+                ELSE
+                   CALL mas_ps_pack
+                   agt_count(jp,ip) = number_of_agents
+                   aindex = agt_count(jp,ip)+1
+                   IF ( aindex > SIZE(grid_agents(jp,ip)%agents) )  THEN
+                      CALL mas_eh_realloc_agents_array (ip,jp)
+                   ENDIF
+                   pack_done = .TRUE.
+                ENDIF
+             ENDIF
+             grid_agents(jp,ip)%agents(aindex) = agent_array(n)
+             agt_count(jp,ip) = aindex
+          ELSE
+             IF ( jp <= nys - 1 )  THEN
+                nr_move_south = nr_move_south+1
+!
+!--             Before agent information is swapped to exchange-array, check
+!--             if enough memory is allocated. If required, reallocate exchange
+!--             array.
+                IF ( nr_move_south > SIZE(move_also_south) )  THEN
+!
+!--                At first, allocate further temporary array to swap agent
+!--                information.
+                   ALLOCATE( temp_ns(SIZE(move_also_south)+NR_2_direction_move))
+                   temp_ns(1:nr_move_south-1) = move_also_south                &
+                                                (1:nr_move_south-1)
+                   DEALLOCATE( move_also_south )
+                   ALLOCATE( move_also_south(SIZE(temp_ns)) )
+                   move_also_south(1:nr_move_south-1) = temp_ns                &
+                                                        (1:nr_move_south-1)
+                   DEALLOCATE( temp_ns )
+                ENDIF
+                move_also_south(nr_move_south) = agent_array(n)
+                IF ( jp == -1 )  THEN
+!
+!--                Apply boundary condition along y
+                   IF ( ibc_mas_ns == 0 )  THEN
+                      move_also_south(nr_move_south)%y =                       &
+                                         move_also_south(nr_move_south)%y      &
+                                       + ( ny + 1 ) * dy
+                      move_also_south(nr_move_south)%origin_y =                &
+                                       move_also_south(nr_move_south)%origin_y &
+                                       + ( ny + 1 ) * dy
+                   ELSEIF ( ibc_mas_ns == 1 )  THEN
+!
+!--                   Agent absorption
+                      move_also_south(nr_move_south)%agent_mask = .FALSE.
+                      deleted_agents = deleted_agents + 1
+                   ENDIF
+                ENDIF
+             ELSEIF ( jp >= nyn+1 )  THEN
+                nr_move_north = nr_move_north+1
+!
+!--             Before agent information is swapped to exchange-array, check
+!--             if enough memory is allocated. If required, reallocate exchange
+!--             array.
+                IF ( nr_move_north > SIZE(move_also_north) )  THEN
+!
+!--                At first, allocate further temporary array to swap agent
+!--                information.
+                   ALLOCATE( temp_ns(SIZE(move_also_north)+NR_2_direction_move))
+                   temp_ns(1:nr_move_north-1) =                                &
+                                move_also_south(1:nr_move_north-1)
+                   DEALLOCATE( move_also_north )
+                   ALLOCATE( move_also_north(SIZE(temp_ns)) )
+                   move_also_north(1:nr_move_north-1) =                        &
+                               temp_ns(1:nr_move_north-1)
+                   DEALLOCATE( temp_ns )
+                ENDIF
+                move_also_north(nr_move_north) = agent_array(n)
+                IF ( jp == ny+1 )  THEN
+!
+!--                Apply boundary condition along y
+                   IF ( ibc_mas_ns == 0 )  THEN
+                      move_also_north(nr_move_north)%y =                       &
+                         move_also_north(nr_move_north)%y                      &
+                       - ( ny + 1 ) * dy
+                      move_also_north(nr_move_north)%origin_y =                &
+                         move_also_north(nr_move_north)%origin_y               &
+                       - ( ny + 1 ) * dy
+                   ELSEIF ( ibc_mas_ns == 1 )  THEN
+!
+!--                   Agent absorption
+                      move_also_north(nr_move_north)%agent_mask = .FALSE.
+                      deleted_agents = deleted_agents + 1
+                   ENDIF
+             move_also_north(nr_move_north) = agent_array(n)
+             IF ( jp == ny+1 )  THEN
+!
+!--             Apply boundary condition along y
+                IF ( ibc_mas_ns == 0 )  THEN
+                   move_also_north(nr_move_north)%y = move_also_north(nr_move_north)%y             &
+                                                      - ( ny + 1 ) * dy
+                   move_also_north(nr_move_north)%origin_y =                                       &
+                                                        move_also_north(nr_move_north)%origin_y    &
+                                                        - ( ny + 1 ) * dy
+                ELSEIF ( ibc_mas_ns == 1 )  THEN
+!
+!--                Agent absorption
+                   move_also_north(nr_move_north)%agent_mask = .FALSE.
+                   deleted_agents = deleted_agents + 1
                 ENDIF
              ENDIF
           ENDIF
+       ENDDO
+       RETURN
+    END SUBROUTINE mas_eh_add_agents_to_gridcell
+       ENDIF
+    ENDDO
+    RETURN
+ END SUBROUTINE mas_eh_add_agents_to_gridcell
 #endif
 #if defined( __parallel )
 !------------------------------------------------------------------------------!
+!--------------------------------------------------------------------------------------------------!
 ! Description:
 ! ------------
+!> After ghost layer agents have been received from neighboring PEs, this
+!> subroutine sorts them into the corresponding grid cells
+!------------------------------------------------------------------------------!
+    SUBROUTINE mas_eh_add_ghost_agents_to_gridcell (agent_array)
+       IMPLICIT NONE
+       INTEGER(iwp) ::  ip     !< grid index (x) of agent
+       INTEGER(iwp) ::  jp     !< grid index (x) of agent
+       INTEGER(iwp) ::  n      !< index variable of agent
+       INTEGER(iwp) ::  aindex !< dummy argument for new number of agents per grid box
+       LOGICAL ::  pack_done !< flag to indicate that packing is done
+       TYPE(agent_type), DIMENSION(:), INTENT(IN)  ::  agent_array !< new agents in a grid box
+       pack_done     = .FALSE.
+       DO n = 1, SIZE(agent_array)
+          IF ( .NOT. agent_array(n)%agent_mask )  CYCLE
+          ip = agent_array(n)%x * ddx
+          jp = agent_array(n)%y * ddy
+          IF ( ip < nxl  .OR.  ip > nxr  .OR.  jp < nys  .OR.  jp > nyn ) THEN
+             number_of_agents = agt_count(jp,ip)
+             agents => grid_agents(jp,ip)%agents(1:number_of_agents)
+             aindex = agt_count(jp,ip)+1
+             IF( aindex > SIZE(grid_agents(jp,ip)%agents) )  THEN
+                IF ( pack_done )  THEN
+!> After ghost layer agents have been received from neighboring PEs, this subroutine sorts them into
+!> the corresponding grid cells
+!--------------------------------------------------------------------------------------------------!
+ SUBROUTINE mas_eh_add_ghost_agents_to_gridcell (agent_array)
+    IMPLICIT NONE
+    INTEGER(iwp) ::  aindex  !< dummy argument for new number of agents per grid box
+    INTEGER(iwp) ::  ip      !< grid index (x) of agent
+    INTEGER(iwp) ::  jp      !< grid index (x) of agent
+    INTEGER(iwp) ::  n       !< index variable of agent
+    LOGICAL ::  pack_done  !< flag to indicate that packing is done
+    TYPE(agent_type), DIMENSION(:), INTENT(IN)  ::  agent_array  !< new agents in a grid box
+    pack_done     = .FALSE.
+    DO  n = 1, SIZE(agent_array)
+       IF ( .NOT. agent_array(n)%agent_mask )  CYCLE
+       ip = agent_array(n)%x * ddx
+       jp = agent_array(n)%y * ddy
+       IF ( ip < nxl  .OR.  ip > nxr  .OR.  jp < nys  .OR.  jp > nyn )  THEN
+          number_of_agents = agt_count(jp,ip)
+          agents => grid_agents(jp,ip)%agents(1:number_of_agents)
+          aindex = agt_count(jp,ip)+1
+          IF( aindex > SIZE( grid_agents(jp,ip)%agents ) )  THEN
+             IF ( pack_done )  THEN
+                CALL mas_eh_realloc_agents_array (ip,jp)
+             ELSE
+                CALL mas_ps_pack
+                agt_count(jp,ip) = number_of_agents
+                aindex = agt_count(jp,ip)+1
+                IF ( aindex > SIZE( grid_agents(jp,ip)%agents ) )  THEN
                    CALL mas_eh_realloc_agents_array (ip,jp)
-                ELSE
-                   CALL mas_ps_pack
-                   agt_count(jp,ip) = number_of_agents
-                   aindex = agt_count(jp,ip)+1
-                   IF ( aindex > SIZE(grid_agents(jp,ip)%agents) )  THEN
-                      CALL mas_eh_realloc_agents_array (ip,jp)
-                   ENDIF
-                   pack_done = .TRUE.
                 ENDIF
+                pack_done = .TRUE.
              ENDIF
-             grid_agents(jp,ip)%agents(aindex) = agent_array(n)
-             agt_count(jp,ip) = aindex
           ENDIF
+       ENDDO
+    END SUBROUTINE mas_eh_add_ghost_agents_to_gridcell
+          grid_agents(jp,ip)%agents(aindex) = agent_array(n)
+          agt_count(jp,ip) = aindex
+       ENDIF
+    ENDDO
+ END SUBROUTINE mas_eh_add_ghost_agents_to_gridcell
 #endif
 !------------------------------------------------------------------------------!
+!--------------------------------------------------------------------------------------------------!
 ! Description:
 ! ------------
 !> Resizing of agent arrays
+!------------------------------------------------------------------------------!
+    SUBROUTINE mas_eh_dealloc_agents_array
+       IMPLICIT NONE
+       INTEGER(iwp) ::  i         !< grid index (x) of agent
+       INTEGER(iwp) ::  j         !< grid index (y) of agent
+       INTEGER(iwp) ::  old_size  !< old array size
+       INTEGER(iwp) ::  new_size  !< new array size
+       INTEGER(iwp) ::  noa       !< number of agents
+       LOGICAL ::  dealloc  !< flag that indicates if reallocation is necessary
+       TYPE(agent_type), DIMENSION(10) ::  tmp_agents_s !< temporary static agent array
+       TYPE(agent_type), DIMENSION(:), ALLOCATABLE ::  tmp_agents_d !< temporary dynamic agent array
+       DO  i = nxlg, nxrg
+          DO  j = nysg, nyng
+!
+!--          Determine number of active agents
+             noa = agt_count(j,i)
+!
+!--          Determine allocated memory size
+             old_size = SIZE( grid_agents(j,i)%agents )
+!
+!--          Check for large unused memory
+             dealloc = ( ( noa < min_nr_agent .AND. old_size  > min_nr_agent ) &
+                    .OR. ( noa > min_nr_agent .AND. old_size - noa *           &
+                         ( 1.0_wp + 0.01_wp * alloc_factor_mas ) > 0.0_wp ) )
+!
+!--          If large unused memory was found, resize the corresponding array
+             IF ( dealloc )  THEN
+                IF ( noa < min_nr_agent )  THEN
+                   new_size = min_nr_agent
+                ELSE
+                   new_size = INT( noa * ( 1.0_wp +                            &
+.01_wp * alloc_factor_mas ) )
+                ENDIF
+                IF ( noa <= 10 )  THEN
+                   tmp_agents_s(1:noa) = grid_agents(j,i)%agents(1:noa)
+                   DEALLOCATE(grid_agents(j,i)%agents)
+                   ALLOCATE(grid_agents(j,i)%agents(1:new_size))
+                   grid_agents(j,i)%agents(1:noa)          = tmp_agents_s(1:noa)
+                   grid_agents(j,i)%agents(noa+1:new_size) = zero_agent
+                ELSE
+                   ALLOCATE(tmp_agents_d(noa))
+                   tmp_agents_d(1:noa) = grid_agents(j,i)%agents(1:noa)
+                   DEALLOCATE(grid_agents(j,i)%agents)
+                   ALLOCATE(grid_agents(j,i)%agents(new_size))
+                   grid_agents(j,i)%agents(1:noa)          = tmp_agents_d(1:noa)
+                   grid_agents(j,i)%agents(noa+1:new_size) = zero_agent
+                   DEALLOCATE(tmp_agents_d)
+                ENDIF
+!--------------------------------------------------------------------------------------------------!
+ SUBROUTINE mas_eh_dealloc_agents_array
+    IMPLICIT NONE
+    INTEGER(iwp) ::  i         !< grid index (x) of agent
+    INTEGER(iwp) ::  j         !< grid index (y) of agent
+    INTEGER(iwp) ::  new_size  !< new array size
+    INTEGER(iwp) ::  noa       !< number of agents
+    INTEGER(iwp) ::  old_size  !< old array size
+    LOGICAL ::  dealloc  !< flag that indicates if reallocation is necessary
+    TYPE(agent_type), DIMENSION(10) ::  tmp_agents_s  !< temporary static agent array
+    TYPE(agent_type), DIMENSION(:), ALLOCATABLE ::  tmp_agents_d  !< temporary dynamic agent array
+    DO  i = nxlg, nxrg
+       DO  j = nysg, nyng
+!
+!--       Determine number of active agents
+          noa = agt_count(j,i)
+!
+!--       Determine allocated memory size
+          old_size = SIZE( grid_agents(j,i)%agents )
+!
+!--       Check for large unused memory
+          dealloc = ( ( noa < min_nr_agent .AND. old_size  > min_nr_agent )  .OR.                  &
+                      ( noa > min_nr_agent .AND.                                                   &
+                        old_size - noa * ( 1.0_wp + 0.01_wp * alloc_factor_mas ) > 0.0_wp )        &
+                    )
+!
+!--       If large unused memory was found, resize the corresponding array
+          IF ( dealloc )  THEN
+             IF ( noa < min_nr_agent )  THEN
+                new_size = min_nr_agent
+             ELSE
+                new_size = INT( noa * ( 1.0_wp + 0.01_wp * alloc_factor_mas ) )
              ENDIF
+          ENDDO
+             IF ( noa <= 10 )  THEN
+                tmp_agents_s(1:noa) = grid_agents(j,i)%agents(1:noa)
+                DEALLOCATE(grid_agents(j,i)%agents)
+                ALLOCATE(grid_agents(j,i)%agents(1:new_size))
+                grid_agents(j,i)%agents(1:noa)          = tmp_agents_s(1:noa)
+                grid_agents(j,i)%agents(noa+1:new_size) = zero_agent
+             ELSE
+                ALLOCATE(tmp_agents_d(noa))
+                tmp_agents_d(1:noa) = grid_agents(j,i)%agents(1:noa)
+                DEALLOCATE(grid_agents(j,i)%agents)
+                ALLOCATE(grid_agents(j,i)%agents(new_size))
+                grid_agents(j,i)%agents(1:noa)          = tmp_agents_d(1:noa)
+                grid_agents(j,i)%agents(noa+1:new_size) = zero_agent
+                DEALLOCATE(tmp_agents_d)
+             ENDIF
+          ENDIF
        ENDDO
+    END SUBROUTINE mas_eh_dealloc_agents_array
+!------------------------------------------------------------------------------!
+    ENDDO
+ END SUBROUTINE mas_eh_dealloc_agents_array
+!--------------------------------------------------------------------------------------------------!
 ! Description:
 ! ------------
 !> Exchange between subdomains.
+!> As soon as one agent has moved beyond the boundary of the domain, it
+!> is included in the relevant transfer arrays and marked for subsequent
+!> deletion on this PE.
+!> First sweep for crossings in x direction. Find out first the number of
+!> agents to be transferred and allocate temporary arrays needed to store
+!> them.
+!> For a one-dimensional decomposition along y, no transfer is necessary,
+!> because the agent remains on the PE, but the agent coordinate has to
+!> be adjusted.
+!------------------------------------------------------------------------------!
+    SUBROUTINE mas_eh_exchange_horiz
+       IMPLICIT NONE
+       INTEGER(iwp) ::  ip               !< index variable along x
+       INTEGER(iwp) ::  jp               !< index variable along y
+       INTEGER(iwp) ::  n                !< agent index variable
+!> As soon as one agent has moved beyond the boundary of the domain, it is included in the relevant
+!> transfer arrays and marked for subsequent deletion on this PE.
+!> First sweep for crossings in x direction. Find out first the number of agents to be transferred
+!> and allocate temporary arrays needed to store them.
+!> For a one-dimensional decomposition along y, no transfer is necessary, because the agent remains
+!> on the PE, but the agent coordinate has to be adjusted.
+!--------------------------------------------------------------------------------------------------!
+ SUBROUTINE mas_eh_exchange_horiz
+    IMPLICIT NONE
+    INTEGER(iwp) ::  ip               !< index variable along x
+    INTEGER(iwp) ::  jp               !< index variable along y
+    INTEGER(iwp) ::  n                !< agent index variable
 #if defined( __parallel )
+       INTEGER(iwp) ::  i                !< grid index (x) of agent positition
+       INTEGER(iwp) ::  j                !< grid index (y) of agent positition
+       INTEGER(iwp) ::  par_size         !< Agent size in bytes
+       INTEGER(iwp) ::  trla_count       !< number of agents send to left PE
+       INTEGER(iwp) ::  trla_count_recv  !< number of agents receive from right PE
+       INTEGER(iwp) ::  trna_count       !< number of agents send to north PE
+       INTEGER(iwp) ::  trna_count_recv  !< number of agents receive from south PE
+       INTEGER(iwp) ::  trra_count       !< number of agents send to right PE
+       INTEGER(iwp) ::  trra_count_recv  !< number of agents receive from left PE
+       INTEGER(iwp) ::  trsa_count       !< number of agents send to south PE
+       INTEGER(iwp) ::  trsa_count_recv  !< number of agents receive from north PE
+       TYPE(agent_type), DIMENSION(:), ALLOCATABLE ::  rvla  !< agents received from right PE
+       TYPE(agent_type), DIMENSION(:), ALLOCATABLE ::  rvna  !< agents received from south PE
+       TYPE(agent_type), DIMENSION(:), ALLOCATABLE ::  rvra  !< agents received from left PE
+       TYPE(agent_type), DIMENSION(:), ALLOCATABLE ::  rvsa  !< agents received from north PE
+       TYPE(agent_type), DIMENSION(:), ALLOCATABLE ::  trla  !< agents send to left PE
+       TYPE(agent_type), DIMENSION(:), ALLOCATABLE ::  trna  !< agents send to north PE
+       TYPE(agent_type), DIMENSION(:), ALLOCATABLE ::  trra  !< agents send to right PE
+       TYPE(agent_type), DIMENSION(:), ALLOCATABLE ::  trsa  !< agents send to south PE
+!
+!--    Exchange between subdomains.
+!--    As soon as one agent has moved beyond the boundary of the domain, it
+!--    is included in the relevant transfer arrays and marked for subsequent
+!--    deletion on this PE.
+!--    First sweep for crossings in x direction. Find out first the number of
+!--    agents to be transferred and allocate temporary arrays needed to store
+!--    them.
+!--    For a one-dimensional decomposition along y, no transfer is necessary,
+!--    because the agent remains on the PE, but the agent coordinate has to
+!--    be adjusted.
+       trla_count  = 0
+       trra_count  = 0
+       trla_count_recv   = 0
+       trra_count_recv   = 0
+       IF ( pdims(1) /= 1 )  THEN
+!
+!--       First calculate the storage necessary for sending and receiving the data.
+!--       Compute only first (nxl) and last (nxr) loop iterration.
+          DO  ip = nxl, nxr, nxr - nxl
+             DO  jp = nys, nyn
+                number_of_agents = agt_count(jp,ip)
+                IF ( number_of_agents <= 0 )  CYCLE
+                agents => grid_agents(jp,ip)%agents(1:number_of_agents)
+                DO  n = 1, number_of_agents
+                   IF ( agents(n)%agent_mask )  THEN
+                      i = agents(n)%x * ddx
+!
+!--                   Above calculation does not work for indices less than zero
+                      IF ( agents(n)%x < 0.0_wp )  i = -1
+                      IF ( i < nxl )  THEN
+                         trla_count = trla_count + 1
+                      ELSEIF ( i > nxr )  THEN
+                         trra_count = trra_count + 1
+                      ENDIF
+                   ENDIF
+                ENDDO
+             ENDDO
+          ENDDO
+          IF ( trla_count  == 0 )  trla_count  = 1
+          IF ( trra_count  == 0 )  trra_count  = 1
+          ALLOCATE( trla(trla_count), trra(trra_count) )
+          trla = zero_agent
+          trra = zero_agent
+          trla_count  = 0
+          trra_count  = 0
+       ENDIF
+!
+!--    Compute only first (nxl) and last (nxr) loop iterration
+       DO  ip = nxl, nxr, nxr-nxl
+    INTEGER(iwp) ::  i                !< grid index (x) of agent positition
+    INTEGER(iwp) ::  j                !< grid index (y) of agent positition
+    INTEGER(iwp) ::  par_size         !< Agent size in bytes
+    INTEGER(iwp) ::  trla_count       !< number of agents send to left PE
+    INTEGER(iwp) ::  trla_count_recv  !< number of agents receive from right PE
+    INTEGER(iwp) ::  trna_count       !< number of agents send to north PE
+    INTEGER(iwp) ::  trna_count_recv  !< number of agents receive from south PE
+    INTEGER(iwp) ::  trra_count       !< number of agents send to right PE
+    INTEGER(iwp) ::  trra_count_recv  !< number of agents receive from left PE
+    INTEGER(iwp) ::  trsa_count       !< number of agents send to south PE
+    INTEGER(iwp) ::  trsa_count_recv  !< number of agents receive from north PE
+    TYPE(agent_type), DIMENSION(:), ALLOCATABLE ::  rvla  !< agents received from right PE
+    TYPE(agent_type), DIMENSION(:), ALLOCATABLE ::  rvna  !< agents received from south PE
+    TYPE(agent_type), DIMENSION(:), ALLOCATABLE ::  rvra  !< agents received from left PE
+    TYPE(agent_type), DIMENSION(:), ALLOCATABLE ::  rvsa  !< agents received from north PE
+    TYPE(agent_type), DIMENSION(:), ALLOCATABLE ::  trla  !< agents send to left PE
+    TYPE(agent_type), DIMENSION(:), ALLOCATABLE ::  trna  !< agents send to north PE
+    TYPE(agent_type), DIMENSION(:), ALLOCATABLE ::  trra  !< agents send to right PE
+    TYPE(agent_type), DIMENSION(:), ALLOCATABLE ::  trsa  !< agents send to south PE
+!
+!-- Exchange between subdomains.
+!-- As soon as one agent has moved beyond the boundary of the domain, it is included in the relevant
+!-- transfer arrays and marked for subsequent deletion on this PE.
+!-- First sweep for crossings in x direction. Find out first the number of agents to be transferred
+!-- and allocate temporary arrays needed to store them.
+!-- For a one-dimensional decomposition along y, no transfer is necessary, because the agent remains
+!-- on the PE, but the agent coordinate has to be adjusted.
+    trla_count  = 0
+    trra_count  = 0
+    trla_count_recv   = 0
+    trra_count_recv   = 0
+    IF ( pdims(1) /= 1 )  THEN
+!
+!--    First calculate the storage necessary for sending and receiving the data.
+!--    Compute only first (nxl) and last (nxr) loop iterration.
+       DO  ip = nxl, nxr, nxr - nxl
           DO  jp = nys, nyn
+             number_of_agents = agt_count(jp,ip)
+             IF ( number_of_agents <= 0 ) CYCLE
+             agents => grid_agents(jp,ip)%agents(1:number_of_agents)
+             DO  n = 1, number_of_agents
+!
+!--             Only those agents that have not been marked as 'deleted' may
+!--             be moved.
+                IF ( agents(n)%agent_mask )  THEN
+                   i = agents(n)%x * ddx
+!
+!--                Above calculation does not work for indices less than zero
+                   IF ( agents(n)%x < 0.0_wp )  i = -1
+                   IF ( i <  nxl )  THEN
+                      IF ( i < 0 )  THEN
+!
+!--                      Apply boundary condition along x
+                         IF ( ibc_mas_lr == 0 )  THEN
+!
+!--                         Cyclic condition
+                            IF ( pdims(1) == 1 )  THEN
+                               agents(n)%x        = ( nx + 1 ) * dx +          &
+                                                    agents(n)%x
+                               agents(n)%origin_x = ( nx + 1 ) * dx +          &
+                                                    agents(n)%origin_x
+                            ELSE
+                               trla_count         = trla_count + 1
+                               trla(trla_count)   = agents(n)
+                               trla(trla_count)%x = ( nx + 1 ) * dx +          &
+                                                    trla(trla_count)%x
+                               trla(trla_count)%origin_x =                     &
+                                                trla(trla_count)%origin_x +    &
+                                                ( nx + 1 ) * dx
+                               agents(n)%agent_mask  = .FALSE.
+                               deleted_agents = deleted_agents + 1
+                               IF ( trla(trla_count)%x >=                      &
+                                        (nx + 1)* dx - 1.0E-12_wp )            &
+                               THEN
+                                  trla(trla_count)%x = trla(trla_count)%x -    &
+.0E-10_wp
+                                  trla(trla_count)%origin_x =                  &
+                                                   trla(trla_count)%origin_x - 1
+                               ENDIF
+                            ENDIF
+                         ELSEIF ( ibc_mas_lr == 1 )  THEN
+!
+!--                         Agent absorption
+                            agents(n)%agent_mask = .FALSE.
+                            deleted_agents = deleted_agents + 1
+                         ENDIF
+                      ELSE
+!
+!--                      Store agent data in the transfer array, which will be
+!--                      send to the neighbouring PE
+                         trla_count = trla_count + 1
+                         trla(trla_count) = agents(n)
+                         agents(n)%agent_mask = .FALSE.
+                         deleted_agents = deleted_agents + 1
+                      ENDIF
+                   ELSEIF ( i > nxr )  THEN
+                      IF ( i > nx )  THEN
+!
+!--                      Apply boundary condition along x
+                         IF ( ibc_mas_lr == 0 )  THEN
+!
+!--                         Cyclic condition
+                            IF ( pdims(1) == 1 )  THEN
+                               agents(n)%x = agents(n)%x - ( nx + 1 ) * dx
+                               agents(n)%origin_x = agents(n)%origin_x - &
+                               ( nx + 1 ) * dx
+                            ELSE
+                               trra_count = trra_count + 1
+                               trra(trra_count) = agents(n)
+                               trra(trra_count)%x = trra(trra_count)%x -       &
+                                                    ( nx + 1 ) * dx
+                               trra(trra_count)%origin_x =                     &
+                                                   trra(trra_count)%origin_x - &
+                                                   ( nx + 1 ) * dx
+                               agents(n)%agent_mask = .FALSE.
+                               deleted_agents = deleted_agents + 1
+                            ENDIF
+                         ELSEIF ( ibc_mas_lr == 1 )  THEN
+!
+!--                         Agent absorption
+                            agents(n)%agent_mask = .FALSE.
+                            deleted_agents = deleted_agents + 1
+                         ENDIF
+                      ELSE
+!
+!--                      Store agent data in the transfer array, which will be send
+!--                      to the neighbouring PE
+                         trra_count = trra_count + 1
+                         trra(trra_count) = agents(n)
+                         agents(n)%agent_mask = .FALSE.
+                         deleted_agents = deleted_agents + 1
+                      ENDIF
+                   ENDIF
+                ENDIF
+             ENDDO
+          ENDDO
+       ENDDO
+!
+!--    Allocate arrays required for north-south exchange, as these
+!--    are used directly after agents are exchange along x-direction.
+       ALLOCATE( move_also_north(1:NR_2_direction_move) )
+       ALLOCATE( move_also_south(1:NR_2_direction_move) )
+       nr_move_north = 0
+       nr_move_south = 0
+!
+!--    Send left boundary, receive right boundary (but first exchange how many
+!--    and chec if agent storage must be extended)
+       IF ( pdims(1) /= 1 )  THEN
+          CALL MPI_SENDRECV( trla_count,      1, MPI_INTEGER, pleft,  0, &
+                             trra_count_recv, 1, MPI_INTEGER, pright, 0, &
+                             comm2d, status, ierr )
+          ALLOCATE(rvra(MAX(1,trra_count_recv)))
+!
+!--       This MPI_SENDRECV should work even with odd mixture on 32 and 64 Bit
+!--       variables in structure agent_type (due to the calculation of par_size)
+          par_size = STORAGE_SIZE(trla(1))/8
+          CALL MPI_SENDRECV( trla, max(1,trla_count)*par_size, MPI_BYTE, pleft,&
+, rvra, max(1,trra_count_recv)*par_size, MPI_BYTE, pright,&
+, comm2d, status, ierr )
+          IF ( trra_count_recv > 0 ) THEN
+             CALL mas_eh_add_agents_to_gridcell(rvra(1:trra_count_recv))
+          ENDIF
+          DEALLOCATE(rvra)
+!
+!--       Send right boundary, receive left boundary
+          CALL MPI_SENDRECV( trra_count,      1, MPI_INTEGER, pright, 0,       &
+                             trla_count_recv, 1, MPI_INTEGER, pleft,  0,       &
+                             comm2d, status, ierr )
+          ALLOCATE(rvla(MAX(1,trla_count_recv)))
+!
+!--       This MPI_SENDRECV should work even with odd mixture on 32 and 64 Bit
+!--       variables in structure agent_type (due to the calculation of par_size)
+          par_size = STORAGE_SIZE(trra(1))/8
+          CALL MPI_SENDRECV( trra, max(1,trra_count)*par_size, MPI_BYTE,       &
+                             pright, 1, rvla,                                  &
+                             max(1,trla_count_recv)*par_size, MPI_BYTE,        &
+                             pleft, 1, comm2d, status, ierr )
+          IF ( trla_count_recv > 0 ) THEN
+             CALL mas_eh_add_agents_to_gridcell(rvla(1:trla_count_recv))
+          ENDIF
+          DEALLOCATE( rvla )
+          DEALLOCATE( trla, trra )
+       ENDIF
+!
+!--    Check whether agents have crossed the boundaries in y direction. Note
+!--    that this case can also apply to agents that have just been received
+!--    from the adjacent right or left PE.
+!--    Find out first the number of agents to be transferred and allocate
+!--    temporary arrays needed to store them.
+!--    For a one-dimensional decomposition along y, no transfer is necessary,
+!--    because the agent remains on the PE.
+       trsa_count  = nr_move_south
+       trna_count  = nr_move_north
+       trsa_count_recv   = 0
+       trna_count_recv   = 0
+       IF ( pdims(2) /= 1 )  THEN
+!
+!--       First calculate the storage necessary for sending and receiving the
+!--       data
+          DO  ip = nxl, nxr
+             DO  jp = nys, nyn, nyn-nys    !compute only first (nys) and last (nyn) loop iterration
+                number_of_agents = agt_count(jp,ip)
+                IF ( number_of_agents <= 0 )  CYCLE
+                agents => grid_agents(jp,ip)%agents(1:number_of_agents)
+                DO  n = 1, number_of_agents
+                   IF ( agents(n)%agent_mask )  THEN
+                      j = agents(n)%y * ddy
+!
+!--                   Above calculation does not work for indices less than zero
+                      IF ( agents(n)%y < 0.0_wp )  j = -1
+                      IF ( j < nys )  THEN
+                         trsa_count = trsa_count + 1
+                      ELSEIF ( j > nyn )  THEN
+                         trna_count = trna_count + 1
+                      ENDIF
+                   ENDIF
+                ENDDO
+             ENDDO
+          ENDDO
+          IF ( trsa_count  == 0 )  trsa_count  = 1
+          IF ( trna_count  == 0 )  trna_count  = 1
+          ALLOCATE( trsa(trsa_count), trna(trna_count) )
+          trsa = zero_agent
+          trna = zero_agent
+          trsa_count  = nr_move_south
+          trna_count  = nr_move_north
+          trsa(1:nr_move_south) = move_also_south(1:nr_move_south)
+          trna(1:nr_move_north) = move_also_north(1:nr_move_north)
+       ENDIF
+       DO  ip = nxl, nxr
+          DO  jp = nys, nyn, nyn-nys ! compute only first (nys) and last (nyn) loop iterration
              number_of_agents = agt_count(jp,ip)
              IF ( number_of_agents <= 0 )  CYCLE
              agents => grid_agents(jp,ip)%agents(1:number_of_agents)
              DO  n = 1, number_of_agents
+!
-!--             Only those agents that have not been marked as 'deleted' may
-!--             be moved.
                 IF ( agents(n)%agent_mask )  THEN
+                   j = agents(n)%y * ddy
+                   i = agents(n)%x * ddx
+!
 !--                Above calculation does not work for indices less than zero
+                   IF ( agents(n)%y < 0.0_wp * dy )  j = -1
+                   IF ( j < nys )  THEN
+                      IF ( j < 0 )  THEN
+!
+!--                      Apply boundary condition along y
+                         IF ( ibc_mas_ns == 0 )  THEN
+!
+!--                         Cyclic condition
+                            IF ( pdims(2) == 1 )  THEN
+                               agents(n)%y = ( ny + 1 ) * dy + agents(n)%y
+                               agents(n)%origin_y = ( ny + 1 ) * dy +          &
+                                                     agents(n)%origin_y
+                            ELSE
+                               trsa_count         = trsa_count + 1
+                               trsa(trsa_count)   = agents(n)
+                               trsa(trsa_count)%y = ( ny + 1 ) * dy +          &
+                                                 trsa(trsa_count)%y
+                               trsa(trsa_count)%origin_y =                     &
+                                                  trsa(trsa_count)%origin_y    &
+                                                + ( ny + 1 ) * dy
+                               agents(n)%agent_mask = .FALSE.
+                               deleted_agents = deleted_agents + 1
+                               IF ( trsa(trsa_count)%y >=                      &
+                                                    (ny+1)* dy - 1.0E-12_wp )  &
+                               THEN
+                                  trsa(trsa_count)%y = trsa(trsa_count)%y -    &
+.0E-10_wp
+                                  trsa(trsa_count)%origin_y =                  &
+                                                  trsa(trsa_count)%origin_y - 1
+                               ENDIF
+                   IF ( agents(n)%x < 0.0_wp )  i = -1
+                   IF ( i < nxl )  THEN
+                      trla_count = trla_count + 1
+                   ELSEIF ( i > nxr )  THEN
+                      trra_count = trra_count + 1
+                   ENDIF
+                ENDIF
+             ENDDO
+          ENDDO
+       ENDDO
+       IF ( trla_count  == 0 )  trla_count  = 1
+       IF ( trra_count  == 0 )  trra_count  = 1
+       ALLOCATE( trla(trla_count), trra(trra_count) )
+       trla = zero_agent
+       trra = zero_agent
+       trla_count  = 0
+       trra_count  = 0
+    ENDIF
+!
+!-- Compute only first (nxl) and last (nxr) loop iterration
+    DO  ip = nxl, nxr, nxr-nxl
+       DO  jp = nys, nyn
+          number_of_agents = agt_count(jp,ip)
+          IF ( number_of_agents <= 0 ) CYCLE
+          agents => grid_agents(jp,ip)%agents(1:number_of_agents)
+          DO  n = 1, number_of_agents
+!
+!--          Only those agents that have not been marked as 'deleted' may be moved.
+             IF ( agents(n)%agent_mask )  THEN
+                i = agents(n)%x * ddx
+!
+!--             Above calculation does not work for indices less than zero
+                IF ( agents(n)%x < 0.0_wp )  i = -1
+                IF ( i <  nxl )  THEN
+                   IF ( i < 0 )  THEN
+!
+!--                   Apply boundary condition along x
+                      IF ( ibc_mas_lr == 0 )  THEN
+!
+!--                      Cyclic condition
+                         IF ( pdims(1) == 1 )  THEN
+                            agents(n)%x        = ( nx + 1 ) * dx + agents(n)%x
+                            agents(n)%origin_x = ( nx + 1 ) * dx + agents(n)%origin_x
+                         ELSE
+                            trla_count         = trla_count + 1
+                            trla(trla_count)   = agents(n)
+                            trla(trla_count)%x = ( nx + 1 ) * dx + trla(trla_count)%x
+                            trla(trla_count)%origin_x = trla(trla_count)%origin_x + ( nx + 1 ) * dx
+                            agents(n)%agent_mask  = .FALSE.
+                            deleted_agents = deleted_agents + 1
+                            IF ( trla(trla_count)%x >= (nx + 1)* dx - 1.0E-12_wp )  THEN
+                               trla(trla_count)%x = trla(trla_count)%x - 1.0E-10_wp
+                               trla(trla_count)%origin_x = trla(trla_count)%origin_x - 1
                             ENDIF
-                         ELSEIF ( ibc_mas_ns == 1 )  THEN
+!
-!--                         Agent absorption
-                            agents(n)%agent_mask = .FALSE.
-                            deleted_agents          = deleted_agents + 1
                          ENDIF
+                      ELSE
+!
+!--                      Store agent data in the transfer array, which will
+!--                      be send to the neighbouring PE
+                         trsa_count = trsa_count + 1
+                         trsa(trsa_count) = agents(n)
+                      ELSEIF ( ibc_mas_lr == 1 )  THEN
+!
+!--                      Agent absorption
                          agents(n)%agent_mask = .FALSE.
                          deleted_agents = deleted_agents + 1
                       ENDIF
+                   ELSEIF ( j > nyn )  THEN
+                      IF ( j > ny )  THEN
+!
+!--                      Apply boundary condition along y
+                         IF ( ibc_mas_ns == 0 )  THEN
+!
+!--                         Cyclic condition
+                            IF ( pdims(2) == 1 )  THEN
+                               agents(n)%y        = agents(n)%y -              &
+                                                    ( ny + 1 ) * dy
+                               agents(n)%origin_y = agents(n)%origin_y -       &
+                                                    ( ny + 1 ) * dy
+                            ELSE
+                               trna_count         = trna_count + 1
+                               trna(trna_count)   = agents(n)
+                               trna(trna_count)%y =                            &
+                                          trna(trna_count)%y - ( ny + 1 ) * dy
+                               trna(trna_count)%origin_y =                     &
+                                         trna(trna_count)%origin_y -           &
+                                         ( ny + 1 ) * dy
+                               agents(n)%agent_mask = .FALSE.
+                               deleted_agents          = deleted_agents + 1
+                            ENDIF
+                         ELSEIF ( ibc_mas_ns == 1 )  THEN
+!
+!--                         Agent absorption
+                   ELSE
+!
+!--                   Store agent data in the transfer array, which will be send to the neighbouring
+!--                   PE.
+                      trla_count = trla_count + 1
+                      trla(trla_count) = agents(n)
+                      agents(n)%agent_mask = .FALSE.
+                      deleted_agents = deleted_agents + 1
+                   ENDIF
+                ELSEIF ( i > nxr )  THEN
+                   IF ( i > nx )  THEN
+!
+!--                   Apply boundary condition along x
+                      IF ( ibc_mas_lr == 0 )  THEN
+!
+!--                      Cyclic condition
+                         IF ( pdims(1) == 1 )  THEN
+                            agents(n)%x = agents(n)%x - ( nx + 1 ) * dx
+                            agents(n)%origin_x = agents(n)%origin_x - ( nx + 1 ) * dx
+                         ELSE
+                            trra_count = trra_count + 1
+                            trra(trra_count) = agents(n)
+                            trra(trra_count)%x = trra(trra_count)%x - ( nx + 1 ) * dx
+                            trra(trra_count)%origin_x = trra(trra_count)%origin_x - ( nx + 1 ) * dx
                             agents(n)%agent_mask = .FALSE.
                             deleted_agents = deleted_agents + 1
                          ENDIF
+                      ELSE
+!
+!--                      Store agent data in the transfer array, which will
+!--                      be send to the neighbouring PE
+                         trna_count = trna_count + 1
+                         trna(trna_count) = agents(n)
+                      ELSEIF ( ibc_mas_lr == 1 )  THEN
+!
+!--                      Agent absorption
                          agents(n)%agent_mask = .FALSE.
                          deleted_agents = deleted_agents + 1
                       ENDIF
+                   ELSE
+!
+!--                   Store agent data in the transfer array, which will be send to the neighbouring
+!--                   PE.
+                      trra_count = trra_count + 1
+                      trra(trra_count) = agents(n)
+                      agents(n)%agent_mask = .FALSE.
+                      deleted_agents = deleted_agents + 1
+                   ENDIF
+                ENDIF
+             ENDIF
+          ENDDO
+       ENDDO
+    ENDDO
+!
+!-- Allocate arrays required for north-south exchange, as these are used directly after agents are
+!-- exchange along x-direction.
+    ALLOCATE( move_also_north(1:nr_2_direction_move) )
+    ALLOCATE( move_also_south(1:nr_2_direction_move) )
+    nr_move_north = 0
+    nr_move_south = 0
+!
+!-- Send left boundary, receive right boundary (but first exchange how many and check if agent
+!-- storage must be extended).
+    IF ( pdims(1) /= 1 )  THEN
+       CALL MPI_SENDRECV( trla_count,      1, MPI_INTEGER, pleft,  0,                              &
+                          trra_count_recv, 1, MPI_INTEGER, pright, 0,                              &
+                          comm2d, status, ierr )
+       ALLOCATE( rvra(MAX( 1,trra_count_recv )) )
+!
+!--    This MPI_SENDRECV should work even with odd mixture on 32 and 64 Bit variables in structure
+!--    agent_type (due to the calculation of par_size)
+       par_size = STORAGE_SIZE( trla(1) ) / 8
+       CALL MPI_SENDRECV( trla, MAX( 1, trla_count ) * par_size,     MPI_BYTE, pleft,  1,          &
+                          rvra, MAX( 1, trra_count_recv )* par_size, MPI_BYTE, pright, 1,          &
+                          comm2d, status, ierr )
+       IF ( trra_count_recv > 0 )  THEN
+          CALL mas_eh_add_agents_to_gridcell(rvra(1:trra_count_recv))
+       ENDIF
+       DEALLOCATE(rvra)
+!
+!--    Send right boundary, receive left boundary
+       CALL MPI_SENDRECV( trra_count,      1, MPI_INTEGER, pright, 0,                              &
+                          trla_count_recv, 1, MPI_INTEGER, pleft,  0,                              &
+                          comm2d, status, ierr )
+       ALLOCATE(rvla(MAX(1,trla_count_recv)))
+!
+!--    This MPI_SENDRECV should work even with odd mixture on 32 and 64 Bit variables in structure
+!--    agent_type (due to the calculation of par_size)
+       par_size = STORAGE_SIZE(trra(1))/8
+       CALL MPI_SENDRECV( trra, MAX( 1, trra_count ) * par_size,   MPI_BYTE, pright, 1,            &
+                          rvla, MAX(1,trla_count_recv) * par_size, MPI_BYTE,  pleft, 1,            &
+                          comm2d, status, ierr )
+       IF ( trla_count_recv > 0 )  THEN
+          CALL mas_eh_add_agents_to_gridcell(rvla(1:trla_count_recv))
+       ENDIF
+       DEALLOCATE( rvla )
+       DEALLOCATE( trla, trra )
+    ENDIF
+!
+!-- Check whether agents have crossed the boundaries in y direction. Note that this case can also
+!-- apply to agents that have just been received from the adjacent right or left PE.
+!-- Find out first the number of agents to be transferred and allocate temporary arrays needed to
+!-- store them.
+!-- For a one-dimensional decomposition along y, no transfer is necessary, because the agent remains
+!-- on the PE.
+    trsa_count  = nr_move_south
+    trna_count  = nr_move_north
+    trsa_count_recv   = 0
+    trna_count_recv   = 0
+    IF ( pdims(2) /= 1 )  THEN
+!
+!--    First calculate the storage necessary for sending and receiving the data.
+       DO  ip = nxl, nxr
+          DO  jp = nys, nyn, nyn-nys    ! compute only first (nys) and last (nyn) loop iterration
+             number_of_agents = agt_count(jp,ip)
+             IF ( number_of_agents <= 0 )  CYCLE
+             agents => grid_agents(jp,ip)%agents(1:number_of_agents)
+             DO  n = 1, number_of_agents
+                IF ( agents(n)%agent_mask )  THEN
+                   j = agents(n)%y * ddy
+!
+!--                Above calculation does not work for indices less than zero
+                   IF ( agents(n)%y < 0.0_wp )  j = -1
+                   IF ( j < nys )  THEN
+                      trsa_count = trsa_count + 1
+                   ELSEIF ( j > nyn )  THEN
+                      trna_count = trna_count + 1
                    ENDIF
                 ENDIF
 …
        ENDDO
+!
+!--    Send front boundary, receive back boundary (but first exchange how many
+!--    and chec if agent storage must be extended)
+       IF ( pdims(2) /= 1 )  THEN
+          CALL MPI_SENDRECV( trsa_count,      1, MPI_INTEGER, psouth, 0,       &
+                             trna_count_recv, 1, MPI_INTEGER, pnorth, 0,       &
+                             comm2d, status, ierr )
+          ALLOCATE(rvna(MAX(1,trna_count_recv)))
+!
+!--       This MPI_SENDRECV should work even with odd mixture on 32 and 64 Bit
+!--       variables in structure agent_type (due to the calculation of par_size)
+          par_size = STORAGE_SIZE(trsa(1))/8
+          CALL MPI_SENDRECV( trsa, trsa_count*par_size, MPI_BYTE,              &
+                             psouth, 1, rvna,                                  &
+                             trna_count_recv*par_size, MPI_BYTE, pnorth, 1,    &
+                             comm2d, status, ierr )
+          IF ( trna_count_recv  > 0 ) THEN
+             CALL mas_eh_add_agents_to_gridcell(rvna(1:trna_count_recv))
+          ENDIF
+          DEALLOCATE(rvna)
+!
+!--       Send back boundary, receive front boundary
+          CALL MPI_SENDRECV( trna_count,      1, MPI_INTEGER, pnorth, 0,       &
+                             trsa_count_recv, 1, MPI_INTEGER, psouth, 0,       &
+                             comm2d, status, ierr )
+          ALLOCATE(rvsa(MAX(1,trsa_count_recv)))
+!
+!--       This MPI_SENDRECV should work even with odd mixture on 32 and 64 Bit
+!--       variables in structure agent_type (due to the calculation of par_size)
+          par_size = STORAGE_SIZE(trna(1))/8
+          CALL MPI_SENDRECV( trna, trna_count*par_size, MPI_BYTE,              &
+                             pnorth, 1, rvsa,                                  &
+                             trsa_count_recv*par_size, MPI_BYTE, psouth, 1,    &
+                             comm2d, status, ierr )
+          IF ( trsa_count_recv > 0 ) THEN
+             CALL mas_eh_add_agents_to_gridcell(rvsa(1:trsa_count_recv))
+          ENDIF
+          DEALLOCATE(rvsa)
+          number_of_agents = number_of_agents + trsa_count_recv
+          DEALLOCATE( trsa, trna )
+       ENDIF
+       DEALLOCATE( move_also_north )
+       DEALLOCATE( move_also_south )
+!
+!--    Accumulate the number of agents transferred between the subdomains)
+       CALL mas_eh_ghost_exchange
+#else
+       DO  ip = nxl, nxr, nxr-nxl
+          DO  jp = nys, nyn
+             number_of_agents = agt_count(jp,ip)
+             IF ( number_of_agents <= 0 )  CYCLE
+             agents => grid_agents(jp,ip)%agents(1:number_of_agents)
+             DO  n = 1, number_of_agents
+!
+!--             Apply boundary conditions
+                IF ( agents(n)%x < 0.0_wp )  THEN
+                   IF ( ibc_mas_lr == 0 )  THEN
+!
+!--                   Cyclic boundary. Relevant coordinate has to be changed.
+                      agents(n)%x = ( nx + 1 ) * dx + agents(n)%x
+                      agents(n)%origin_x = ( nx + 1 ) * dx + &
+                                  agents(n)%origin_x
+                   ELSEIF ( ibc_mas_lr == 1 )  THEN
+!
+!--                   Agent absorption
+       IF ( trsa_count  == 0 )  trsa_count  = 1
+       IF ( trna_count  == 0 )  trna_count  = 1
+       ALLOCATE( trsa(trsa_count), trna(trna_count) )
+       trsa = zero_agent
+       trna = zero_agent
+       trsa_count  = nr_move_south
+       trna_count  = nr_move_north
+       trsa(1:nr_move_south) = move_also_south(1:nr_move_south)
+       trna(1:nr_move_north) = move_also_north(1:nr_move_north)
+    ENDIF
+    DO  ip = nxl, nxr
+       DO  jp = nys, nyn, nyn-nys ! compute only first (nys) and last (nyn) loop iterration
+          number_of_agents = agt_count(jp,ip)
+          IF ( number_of_agents <= 0 )  CYCLE
+          agents => grid_agents(jp,ip)%agents(1:number_of_agents)
+          DO  n = 1, number_of_agents
+!
+!--          Only those agents that have not been marked as 'deleted' may be moved.
+             IF ( agents(n)%agent_mask )  THEN
+                j = agents(n)%y * ddy
+!
+!--             Above calculation does not work for indices less than zero
+                IF ( agents(n)%y < 0.0_wp * dy )  j = -1
+                IF ( j < nys )  THEN
+                   IF ( j < 0 )  THEN
+!
+!--                   Apply boundary condition along y
+                      IF ( ibc_mas_ns == 0 )  THEN
+!
+!--                      Cyclic condition
+                         IF ( pdims(2) == 1 )  THEN
+                            agents(n)%y = ( ny + 1 ) * dy + agents(n)%y
+                            agents(n)%origin_y = ( ny + 1 ) * dy + agents(n)%origin_y
+                         ELSE
+                            trsa_count         = trsa_count + 1
+                            trsa(trsa_count)   = agents(n)
+                            trsa(trsa_count)%y = ( ny + 1 ) * dy + trsa(trsa_count)%y
+                            trsa(trsa_count)%origin_y = trsa(trsa_count)%origin_y + ( ny + 1 ) * dy
+                            agents(n)%agent_mask = .FALSE.
+                            deleted_agents = deleted_agents + 1
+                            IF ( trsa(trsa_count)%y >= (ny+1)* dy - 1.0E-12_wp )  THEN
+                               trsa(trsa_count)%y = trsa(trsa_count)%y - 1.0E-10_wp
+                               trsa(trsa_count)%origin_y = trsa(trsa_count)%origin_y - 1
+                            ENDIF
+                         ENDIF
+                      ELSEIF ( ibc_mas_ns == 1 )  THEN
+!
+!--                      Agent absorption
+                         agents(n)%agent_mask = .FALSE.
+                         deleted_agents          = deleted_agents + 1
+                      ENDIF
+                   ELSE
+!
+!--                   Store agent data in the transfer array, which will be send to the neighbouring
+!--                   PE.
+                      trsa_count = trsa_count + 1
+                      trsa(trsa_count) = agents(n)
                       agents(n)%agent_mask = .FALSE.
                       deleted_agents = deleted_agents + 1
                    ENDIF
+                ELSEIF ( agents(n)%x >= ( nx + 1 ) * dx )  THEN
+                   IF ( ibc_mas_lr == 0 )  THEN
+!
+!--                   Cyclic boundary. Relevant coordinate has to be changed.
+                      agents(n)%x = agents(n)%x - ( nx + 1 ) * dx
+                   ELSEIF ( ibc_mas_lr == 1 )  THEN
+!
+!--                   Agent absorption
+                ELSEIF ( j > nyn )  THEN
+                   IF ( j > ny )  THEN
+!
+!--                   Apply boundary condition along y
+                      IF ( ibc_mas_ns == 0 )  THEN
+!
+!--                      Cyclic condition
+                         IF ( pdims(2) == 1 )  THEN
+                            agents(n)%y        = agents(n)%y        - ( ny + 1 ) * dy
+                            agents(n)%origin_y = agents(n)%origin_y - ( ny + 1 ) * dy
+                         ELSE
+                            trna_count         = trna_count + 1
+                            trna(trna_count)   = agents(n)
+                            trna(trna_count)%y = trna(trna_count)%y - ( ny + 1 ) * dy
+                            trna(trna_count)%origin_y = trna(trna_count)%origin_y - ( ny + 1 ) * dy
+                            agents(n)%agent_mask = .FALSE.
+                            deleted_agents          = deleted_agents + 1
+                         ENDIF
+                      ELSEIF ( ibc_mas_ns == 1 )  THEN
+!
+!--                      Agent absorption
+                         agents(n)%agent_mask = .FALSE.
+                         deleted_agents = deleted_agents + 1
+                      ENDIF
+                   ELSE
+!
+!--                   Store agent data in the transfer array, which will be send to the neighbouring
+!--                   PE
+                      trna_count = trna_count + 1
+                      trna(trna_count) = agents(n)
                       agents(n)%agent_mask = .FALSE.
                       deleted_agents = deleted_agents + 1
                    ENDIF
+                ENDIF
+             ENDIF
+          ENDDO
+       ENDDO
+    ENDDO
+!
+!-- Send front boundary, receive back boundary (but first exchange how many and check if agent
+!-- storage must be extended).
+    IF ( pdims(2) /= 1 )  THEN
+       CALL MPI_SENDRECV( trsa_count,      1, MPI_INTEGER, psouth, 0,                              &
+                          trna_count_recv, 1, MPI_INTEGER, pnorth, 0,                              &
+                          comm2d, status, ierr )
+       ALLOCATE( rvna( MAX( 1, trna_count_recv )) )
+!
+!--    This MPI_SENDRECV should work even with odd mixture on 32 and 64 Bit variables in structure
+!--    agent_type (due to the calculation of par_size)
+       par_size = STORAGE_SIZE(trsa(1))/8
+       CALL MPI_SENDRECV( trsa, trsa_count * par_size,      MPI_BYTE, psouth, 1,                   &
+                          rvna, trna_count_recv * par_size, MPI_BYTE, pnorth, 1,                   &
+                          comm2d, status, ierr )
+       IF ( trna_count_recv  > 0 )  THEN
+          CALL mas_eh_add_agents_to_gridcell(rvna(1:trna_count_recv))
+       ENDIF
+       DEALLOCATE( rvna )
+!
+!--    Send back boundary, receive front boundary
+       CALL MPI_SENDRECV( trna_count,      1, MPI_INTEGER, pnorth, 0,                              &
+                          trsa_count_recv, 1, MPI_INTEGER, psouth, 0,                              &
+                          comm2d, status, ierr )
+       ALLOCATE( rvsa( MAX( 1, trsa_count_recv )) )
+!
+!--    This MPI_SENDRECV should work even with odd mixture on 32 and 64 Bit variables in structure
+!--    agent_type (due to the calculation of par_size)
+       par_size = STORAGE_SIZE( trna(1) ) / 8
+       CALL MPI_SENDRECV( trna, trna_count * par_size,      MPI_BYTE, pnorth, 1,                   &
+                          rvsa, trsa_count_recv * par_size, MPI_BYTE, psouth, 1,                   &
+                          comm2d, status, ierr )
+       IF ( trsa_count_recv > 0 )  THEN
+          CALL mas_eh_add_agents_to_gridcell(rvsa(1:trsa_count_recv))
+       ENDIF
+       DEALLOCATE( rvsa )
+       number_of_agents = number_of_agents + trsa_count_recv
+       DEALLOCATE( trsa, trna )
+    ENDIF
+    DEALLOCATE( move_also_north )
+    DEALLOCATE( move_also_south )
+!
+!-- Accumulate the number of agents transferred between the subdomains)
+    CALL mas_eh_ghost_exchange
+#else
+    DO  ip = nxl, nxr, nxr-nxl
+       DO  jp = nys, nyn
+          number_of_agents = agt_count(jp,ip)
+          IF ( number_of_agents <= 0 )  CYCLE
+          agents => grid_agents(jp,ip)%agents(1:number_of_agents)
+          DO  n = 1, number_of_agents
+!
+!--          Apply boundary conditions
+             IF ( agents(n)%x < 0.0_wp )  THEN
+                IF ( ibc_mas_lr == 0 )  THEN
+!
+!--                Cyclic boundary. Relevant coordinate has to be changed.
+                   agents(n)%x = ( nx + 1 ) * dx + agents(n)%x
+                   agents(n)%origin_x = ( nx + 1 ) * dx + agents(n)%origin_x
+                ELSEIF ( ibc_mas_lr == 1 )  THEN
+!
+!--                Agent absorption
+                   agents(n)%agent_mask = .FALSE.
+                   deleted_agents = deleted_agents + 1
+                ENDIF
+             ELSEIF ( agents(n)%x >= ( nx + 1 ) * dx )  THEN
+                IF ( ibc_mas_lr == 0 )  THEN
+!
+!--                Cyclic boundary. Relevant coordinate has to be changed.
+                   agents(n)%x = agents(n)%x - ( nx + 1 ) * dx
+                ELSEIF ( ibc_mas_lr == 1 )  THEN
+!
+!--                Agent absorption
+                   agents(n)%agent_mask = .FALSE.
+                   deleted_agents = deleted_agents + 1
+                ENDIF
+             ENDIF
+          ENDDO
+       ENDDO
+    ENDDO
+    DO  ip = nxl, nxr
+       DO  jp = nys, nyn, nyn-nys
+          number_of_agents = agt_count(jp,ip)
+          IF ( number_of_agents <= 0 )  CYCLE
+          agents => grid_agents(jp,ip)%agents(1:number_of_agents)
+          DO  n = 1, number_of_agents
+             IF ( agents(n)%y < 0.0_wp )  THEN
+                IF ( ibc_mas_ns == 0 )  THEN
+!
+!--                Cyclic boundary. Relevant coordinate has to be changed.
+                   agents(n)%y = ( ny + 1 ) * dy + agents(n)%y
+                   agents(n)%origin_y = ( ny + 1 ) * dy + &
+                        agents(n)%origin_y
+                ELSEIF ( ibc_mas_ns == 1 )  THEN
+!
+!--                Agent absorption
+                   agents(n)%agent_mask = .FALSE.
+                   deleted_agents = deleted_agents + 1
+                ENDIF
+             ELSEIF ( agents(n)%y >= ( ny + 0.5_wp ) * dy )  THEN
+                IF ( ibc_mas_ns == 0 )  THEN
+!
+!--                Cyclic boundary. Relevant coordinate has to be changed.
+                   agents(n)%y = agents(n)%y - ( ny + 1 ) * dy
+                ELSEIF ( ibc_mas_ns == 1 )  THEN
+!
+!--                Agent absorption
+                   agents(n)%agent_mask = .FALSE.
+                   deleted_agents = deleted_agents + 1
+                ENDIF
+             ENDIF
+          ENDDO
+       ENDDO
+    ENDDO
+#endif
+ END SUBROUTINE mas_eh_exchange_horiz
+#if defined( __parallel )
+!--------------------------------------------------------------------------------------------------!
+! Description:
+! ------------
+!> Sends the agents from the three gridcells closest to the north/south/left/right border of a PE to
+!> the corresponding neighbors ghost layer (which is three grid boxes deep)
+!--------------------------------------------------------------------------------------------------!
+ SUBROUTINE mas_eh_ghost_exchange
+    IMPLICIT NONE
+    INTEGER(iwp) ::  agt_size    !< Bit size of agent datatype
+    INTEGER(iwp) ::  ghla_count  !< ghost points left agent
+    INTEGER(iwp) ::  ghna_count  !< ghost points north agent
+    INTEGER(iwp) ::  ghra_count  !< ghost points right agent
+    INTEGER(iwp) ::  ghsa_count  !< ghost points south agent
+    INTEGER(iwp) ::  ip          !< index variable along x
+    INTEGER(iwp) ::  jp          !< index variable along y
+    LOGICAL ::  ghla_empty      !< ghost points left agent
+    LOGICAL ::  ghla_empty_rcv  !< ghost points left agent
+    LOGICAL ::  ghna_empty      !< ghost points north agent
+    LOGICAL ::  ghna_empty_rcv  !< ghost points north agent
+    LOGICAL ::  ghra_empty      !< ghost points right agent
+    LOGICAL ::  ghra_empty_rcv  !< ghost points right agent
+    LOGICAL ::  ghsa_empty      !< ghost points south agent
+    LOGICAL ::  ghsa_empty_rcv  !< ghost points south agent
+    TYPE(agent_type), DIMENSION(:), ALLOCATABLE ::  ghla  !< agents received from right PE
+    TYPE(agent_type), DIMENSION(:), ALLOCATABLE ::  ghna  !< agents received from south PE
+    TYPE(agent_type), DIMENSION(:), ALLOCATABLE ::  ghra  !< agents received from left PE
+    TYPE(agent_type), DIMENSION(:), ALLOCATABLE ::  ghsa  !< agents received from north PE
+    ghla_empty = .TRUE.
+    ghna_empty = .TRUE.
+    ghra_empty = .TRUE.
+    ghsa_empty = .TRUE.
+!
+!-- Reset ghost layer
+    DO  ip = nxlg, nxl-1
+       DO  jp = nysg, nyng
+          agt_count(jp,ip) = 0
+       ENDDO
+    ENDDO
+    DO  ip = nxr+1, nxrg
+       DO  jp = nysg, nyng
+          agt_count(jp,ip) = 0
+       ENDDO
+    ENDDO
+    DO  ip = nxl, nxr
+       DO  jp = nysg, nys-1
+          agt_count(jp,ip) = 0
+       ENDDO
+    ENDDO
+    DO  ip = nxl, nxr
+       DO  jp = nyn+1, nyng
+          agt_count(jp,ip) = 0
+       ENDDO
+    ENDDO
+!
+!-- Transfer of agents from left to right and vice versa
+    IF ( pdims(1) /= 1 )  THEN
+!
+!--    Reset left and right ghost layers
+       ghla_count  = 0
+       ghra_count  = 0
+!
+!--    First calculate the storage necessary for sending and receiving the data.
+       ghla_count = SUM(agt_count(nys:nyn,nxl:nxl+2))
+       ghra_count = SUM(agt_count(nys:nyn,nxr-2:nxr))
+!
+!--    No cyclic boundaries for agents
+       IF ( nxl == 0  .OR.  ghla_count == 0 )  THEN
+          ghla_count = 1
+       ELSE
+          ghla_empty = .FALSE.
+       ENDIF
+       IF ( nxr == nx  .OR.  ghra_count == 0 )  THEN
+          ghra_count = 1
+       ELSE
+          ghra_empty = .FALSE.
+       ENDIF
+       ALLOCATE( ghla(1:ghla_count), ghra(1:ghra_count) )
+       ghla = zero_agent
+       ghra = zero_agent
+!
+!--    Get all agents that will be sent left into one array
+       ghla_count = 0
+       IF ( nxl /= 0 )  THEN
+          DO  ip = nxl, nxl+2
+             DO jp = nys, nyn
+                number_of_agents = agt_count(jp,ip)
+                IF ( number_of_agents <= 0 )  CYCLE
+                ghla(ghla_count+1:ghla_count+number_of_agents)                                     &
+                                                     = grid_agents(jp,ip)%agents(1:number_of_agents)
+                ghla_count = ghla_count + number_of_agents
+             ENDDO
+          ENDDO
+       ENDIF
+       IF ( ghla_count == 0 )  ghla_count = 1
+!
+!--    Get all agents that will be sent right into one array
+       ghra_count = 0
+       IF ( nxr /= nx )  THEN
+          DO  ip = nxr-2, nxr
+             DO  jp = nys, nyn
+                number_of_agents = agt_count(jp,ip)
+                IF ( number_of_agents <= 0 )  CYCLE
+                ghra(ghra_count+1:ghra_count+number_of_agents)                                     &
+                                                   = grid_agents(jp,ip)%agents(1:number_of_agents)
+                ghra_count = ghra_count + number_of_agents
+             ENDDO
+          ENDDO
+       ENDIF
+       IF ( ghra_count == 0 ) ghra_count = 1
+!
+!--    Send/receive number of agents that will be transferred to/from left/right neighbor.
+       CALL MPI_SENDRECV( ghla_count,      1, MPI_INTEGER, pleft,  0,                              &
+                          ghra_count_recv, 1, MPI_INTEGER, pright, 0,                              &
+                          comm2d, status, ierr )
+       ALLOCATE ( agt_gh_r(1:ghra_count_recv) )
+!
+!--    Send/receive number of agents that will be transferred to/from right/left neighbor
+       CALL MPI_SENDRECV( ghra_count,      1, MPI_INTEGER, pright,  0,                             &
+                          ghla_count_recv, 1, MPI_INTEGER, pleft,   0,                             &
+                          comm2d, status, ierr )
+!
+!--    Send/receive flag that indicates if there are actually any agents in ghost layer
+       CALL MPI_SENDRECV( ghla_empty,     1, MPI_LOGICAL, pleft, 1,                                &
+                          ghra_empty_rcv, 1, MPI_LOGICAL, pright,1,                                &
+                          comm2d, status, ierr )
+       CALL MPI_SENDRECV( ghra_empty,     1, MPI_LOGICAL, pright,1,                                &
+                          ghla_empty_rcv, 1, MPI_LOGICAL, pleft, 1,                                &
+                          comm2d, status, ierr )
+       ALLOCATE ( agt_gh_l(1:ghla_count_recv) )
+!
+!--    Get bit size of one agent
+       agt_size = STORAGE_SIZE(zero_agent)/8
+!
+!--    Send/receive agents to/from left/right neighbor
+       CALL MPI_SENDRECV( ghla,     ghla_count      * agt_size, MPI_BYTE, pleft, 1,                &
+                          agt_gh_r, ghra_count_recv * agt_size, MPI_BYTE, pright,1,                &
+                          comm2d, status, ierr )
+!
+!--    Send/receive agents to/from left/right neighbor
+       CALL MPI_SENDRECV( ghra,     ghra_count      * agt_size, MPI_BYTE, pright,1,                &
+                          agt_gh_l, ghla_count_recv * agt_size, MPI_BYTE, pleft, 1,                &
+                          comm2d, status, ierr )
+!
+!--    If agents were received, add them to the respective ghost layer cells
+       IF ( .NOT. ghra_empty_rcv )  THEN
+          CALL mas_eh_add_ghost_agents_to_gridcell(agt_gh_r)
+       ENDIF
+       IF ( .NOT. ghla_empty_rcv )  THEN
+          CALL mas_eh_add_ghost_agents_to_gridcell(agt_gh_l)
+       ENDIF
+       DEALLOCATE( ghla, ghra, agt_gh_l, agt_gh_r )
+    ENDIF
+!
+!-- Transfer of agents from south to north and vice versa
+    IF ( pdims(2) /= 1 )  THEN
+!
+!--    Reset south and north ghost layers
+       ghsa_count  = 0
+       ghna_count  = 0
+!
+!--    First calculate the storage necessary for sending and receiving the data.
+       ghsa_count = SUM( agt_count(nys:nys+2,nxlg:nxrg) )
+       ghna_count = SUM( agt_count(nyn-2:nyn,nxlg:nxrg) )
+!
+!--    No cyclic boundaries for agents
+       IF ( nys == 0  .OR.  ghsa_count == 0 )  THEN
+          ghsa_count = 1
+       ELSE
+          ghsa_empty = .FALSE.
+       ENDIF
+       IF ( nyn == ny  .OR.  ghna_count == 0 )  THEN
+          ghna_count = 1
+       ELSE
+          ghna_empty = .FALSE.
+       ENDIF
+       ALLOCATE( ghsa(1:ghsa_count), ghna(1:ghna_count) )
+       ghsa = zero_agent
+       ghna = zero_agent
+!
+!--    Get all agents that will be sent south into one array
+       ghsa_count = 0
+       IF ( nys /= 0 )  THEN
+          DO  ip = nxlg, nxrg
+             DO  jp = nys, nys+2
+                number_of_agents = agt_count(jp,ip)
+                IF ( number_of_agents <= 0 )  CYCLE
+                ghsa(ghsa_count+1:ghsa_count+number_of_agents)                                     &
+                                                    = grid_agents(jp,ip)%agents(1:number_of_agents)
+                ghsa_count = ghsa_count + number_of_agents
+             ENDDO
+          ENDDO
+       ENDIF
+       IF ( ghsa_count == 0 )  ghsa_count = 1
+!
+!--    Get all agents that will be sent north into one array
+       ghna_count = 0
+       IF ( nyn /= ny )  THEN
+          DO  ip = nxlg, nxrg
+             DO  jp = nyn-2, nyn
+                number_of_agents = agt_count(jp,ip)
+                IF ( number_of_agents <= 0 )  CYCLE
+                ghna(ghna_count+1:ghna_count+number_of_agents)                                     &
+                                                     = grid_agents(jp,ip)%agents(1:number_of_agents)
+                ghna_count = ghna_count + number_of_agents
+             ENDDO
+          ENDDO
+       ENDIF
+       IF ( ghna_count == 0 ) ghna_count = 1
+!
+!--    Send/receive number of agents that will be transferred to/from south/north neighbor
+       CALL MPI_SENDRECV( ghsa_count,        1, MPI_INTEGER, psouth, 0,                            &
+                          ghna_count_recv,   1, MPI_INTEGER, pnorth, 0,                            &
+                          comm2d, status, ierr )
+       ALLOCATE ( agt_gh_n(1:ghna_count_recv) )
+!
+!--    Send/receive number of agents that will be transferred to/from north/south neighbor
+       CALL MPI_SENDRECV( ghna_count,        1, MPI_INTEGER, pnorth, 0,                            &
+                          ghsa_count_recv,   1, MPI_INTEGER, psouth, 0,                            &
+                          comm2d, status, ierr )
+!
+!--    Send/receive flag that indicates if there are actually any agents in ghost layer
+       CALL MPI_SENDRECV( ghsa_empty,     1, MPI_LOGICAL, psouth, 1,                               &
+                          ghna_empty_rcv, 1, MPI_LOGICAL, pnorth, 1,                               &
+                          comm2d, status, ierr )
+       CALL MPI_SENDRECV( ghna_empty,     1, MPI_LOGICAL, pnorth, 1,                               &
+                          ghsa_empty_rcv, 1, MPI_LOGICAL, psouth, 1,                               &
+                          comm2d, status, ierr )
+       ALLOCATE ( agt_gh_s(1:ghsa_count_recv) )
+!
+!--    Get bit size of one agent
+       agt_size = STORAGE_SIZE(zero_agent)/8
+!
+!--    Send/receive agents to/from south/north neighbor
+       CALL MPI_SENDRECV( ghsa,     ghsa_count      * agt_size, MPI_BYTE, psouth,1,                &
+                          agt_gh_n, ghna_count_recv * agt_size, MPI_BYTE, pnorth,1,                &
+                          comm2d, status, ierr )
+!
+!--       Send/receive agents to/from south/north neighbor
+       CALL MPI_SENDRECV( ghna,     ghna_count      * agt_size, MPI_BYTE, pnorth,1,                &
+                          agt_gh_s, ghsa_count_recv * agt_size, MPI_BYTE, psouth,1,                &
+                          comm2d, status, ierr )
+!
+!--    If agents were received, add them to the respective ghost layer cells
+       IF ( .NOT. ghna_empty_rcv )  THEN
+          CALL mas_eh_add_ghost_agents_to_gridcell(agt_gh_n)
+       ENDIF
+       IF ( .NOT. ghsa_empty_rcv )  THEN
+          CALL mas_eh_add_ghost_agents_to_gridcell(agt_gh_s)
+       ENDIF
+       DEALLOCATE( ghna, ghsa, agt_gh_n, agt_gh_s )
+    ENDIF
+ END SUBROUTINE mas_eh_ghost_exchange
+#endif
+!--------------------------------------------------------------------------------------------------!
+! Description:
+! ------------
+!> If an agent moves from one grid cell to another (on the current processor!), this subroutine
+!> moves the corresponding element from the agent array of the old grid cell to the agent array of
+!> the new grid cell.
+!--------------------------------------------------------------------------------------------------!
+ SUBROUTINE mas_eh_move_agent
+    IMPLICIT NONE
+    INTEGER(iwp) ::  aindex         !< dummy argument for number of new agent per grid box
+    INTEGER(iwp) ::  i              !< grid index (x) of agent position
+    INTEGER(iwp) ::  ip             !< index variable along x
+    INTEGER(iwp) ::  j              !< grid index (y) of agent position
+    INTEGER(iwp) ::  jp             !< index variable along y
+    INTEGER(iwp) ::  n              !< index variable for agent array
+    INTEGER(iwp) ::  na_before_move !< number of agents per grid box before moving
+    TYPE(agent_type), DIMENSION(:), POINTER ::  agents_before_move !< agents before moving
+    DO  ip = nxl, nxr
+       DO  jp = nys, nyn
+             na_before_move = agt_count(jp,ip)
+             IF ( na_before_move <= 0 )  CYCLE
+             agents_before_move => grid_agents(jp,ip)%agents(1:na_before_move)
+             DO  n = 1, na_before_move
+                i = agents_before_move(n)%x * ddx
+                j = agents_before_move(n)%y * ddy
+!--             For mas_eh_exchange_horiz to work properly agents need to be moved to the outermost
+!--             gridboxes of the respective processor.
+!--             If the agent index is inside the processor the following lines will not change the
+!--             index.
+                i = MIN ( i , nxr )
+                i = MAX ( i , nxl )
+                j = MIN ( j , nyn )
+                j = MAX ( j , nys )
+!
+!--             Check if agent has moved to another grid cell.
+                IF ( i /= ip  .OR.  j /= jp )  THEN
+!
+!--                If the agent stays on the same processor, the agent will be added to the agent
+!--                array of the new processor.
+                   number_of_agents = agt_count(j,i)
+                   agents => grid_agents(j,i)%agents(1:number_of_agents)
+                   aindex = number_of_agents+1
+                   IF (  aindex > SIZE(grid_agents(j,i)%agents)  )  THEN
+                      CALL mas_eh_realloc_agents_array(i,j)
+                   ENDIF
+                   grid_agents(j,i)%agents(aindex) = agents_before_move(n)
+                   agt_count(j,i) = aindex
+                   agents_before_move(n)%agent_mask = .FALSE.
                 ENDIF
              ENDDO
+          ENDDO
        ENDDO
+       DO  ip = nxl, nxr
+          DO  jp = nys, nyn, nyn-nys
+             number_of_agents = agt_count(jp,ip)
+             IF ( number_of_agents <= 0 )  CYCLE
+             agents => grid_agents(jp,ip)%agents(1:number_of_agents)
+             DO  n = 1, number_of_agents
+                IF ( agents(n)%y < 0.0_wp )  THEN
+                   IF ( ibc_mas_ns == 0 )  THEN
+!
+!--                   Cyclic boundary. Relevant coordinate has to be changed.
+                      agents(n)%y = ( ny + 1 ) * dy + agents(n)%y
+                      agents(n)%origin_y = ( ny + 1 ) * dy + &
+                           agents(n)%origin_y
+                   ELSEIF ( ibc_mas_ns == 1 )  THEN
+!
+!--                   Agent absorption
+                      agents(n)%agent_mask = .FALSE.
+                      deleted_agents = deleted_agents + 1
+                   ENDIF
+                ELSEIF ( agents(n)%y >= ( ny + 0.5_wp ) * dy )  THEN
+                   IF ( ibc_mas_ns == 0 )  THEN
+!
+!--                   Cyclic boundary. Relevant coordinate has to be changed.
+                      agents(n)%y = agents(n)%y - ( ny + 1 ) * dy
+                   ELSEIF ( ibc_mas_ns == 1 )  THEN
+!
+!--                   Agent absorption
+                      agents(n)%agent_mask = .FALSE.
+                      deleted_agents = deleted_agents + 1
+                   ENDIF
+                ENDIF
+             ENDDO
+          ENDDO
+       ENDDO
+#endif
+    END SUBROUTINE mas_eh_exchange_horiz
+#if defined( __parallel )
+!------------------------------------------------------------------------------!
+    ENDDO
+    RETURN
+ END SUBROUTINE mas_eh_move_agent
+!--------------------------------------------------------------------------------------------------!
 ! Description:
 ! ------------
 !> Sends the agents from the three gridcells closest to the
 !> north/south/left/right border of a PE to the corresponding neighbors ghost
 !> layer (which is three grid boxes deep)
 !------------------------------------------------------------------------------!
     SUBROUTINE mas_eh_ghost_exchange
+!> If the allocated memory for the agent array does not suffice to add arriving agents from
+!> neighbour grid cells, this subrouting reallocates the agent array to assure enough memory is
+!> available.
+!--------------------------------------------------------------------------------------------------!
+    SUBROUTINE mas_eh_realloc_agents_array (i,j,size_in)
        IMPLICIT NONE
+       INTEGER(iwp) ::  ip          !< index variable along x
+       INTEGER(iwp) ::  jp          !< index variable along y
+       INTEGER(iwp) ::  agt_size    !< Bit size of agent datatype
+       INTEGER(iwp) ::  ghla_count  !< ghost points left agent
+       INTEGER(iwp) ::  ghna_count  !< ghost points north agent
+       INTEGER(iwp) ::  ghra_count  !< ghost points right agent
+       INTEGER(iwp) ::  ghsa_count  !< ghost points south agent
+       LOGICAL ::  ghla_empty      !< ghost points left agent
+       LOGICAL ::  ghla_empty_rcv  !< ghost points left agent
+       LOGICAL ::  ghna_empty      !< ghost points north agent
+       LOGICAL ::  ghna_empty_rcv  !< ghost points north agent
+       LOGICAL ::  ghra_empty      !< ghost points right agent
+       LOGICAL ::  ghra_empty_rcv  !< ghost points right agent
+       LOGICAL ::  ghsa_empty      !< ghost points south agent
+       LOGICAL ::  ghsa_empty_rcv  !< ghost points south agent
+       TYPE(agent_type), DIMENSION(:), ALLOCATABLE ::  ghla  !< agents received from right PE
+       TYPE(agent_type), DIMENSION(:), ALLOCATABLE ::  ghna  !< agents received from south PE
+       TYPE(agent_type), DIMENSION(:), ALLOCATABLE ::  ghra  !< agents received from left PE
+       TYPE(agent_type), DIMENSION(:), ALLOCATABLE ::  ghsa  !< agents received from north PE
+       ghla_empty = .TRUE.
+       ghna_empty = .TRUE.
+       ghra_empty = .TRUE.
+       ghsa_empty = .TRUE.
+!
+!--    reset ghost layer
+       DO ip = nxlg, nxl-1
+          DO jp = nysg, nyng
+             agt_count(jp,ip) = 0
+          ENDDO
+       ENDDO
+       DO ip = nxr+1, nxrg
+          DO jp = nysg, nyng
+             agt_count(jp,ip) = 0
+          ENDDO
+       ENDDO
+       DO ip = nxl, nxr
+          DO jp = nysg, nys-1
+             agt_count(jp,ip) = 0
+          ENDDO
+       ENDDO
+       DO ip = nxl, nxr
+          DO jp = nyn+1, nyng
+             agt_count(jp,ip) = 0
+          ENDDO
+       ENDDO
+!
+!--    Transfer of agents from left to right and vice versa
+       IF ( pdims(1) /= 1 )  THEN
+!
+!--       Reset left and right ghost layers
+          ghla_count  = 0
+          ghra_count  = 0
+!
+!--       First calculate the storage necessary for sending
+!--       and receiving the data.
+          ghla_count = SUM(agt_count(nys:nyn,nxl:nxl+2))
+          ghra_count = SUM(agt_count(nys:nyn,nxr-2:nxr))
+!
+!--       No cyclic boundaries for agents
+          IF ( nxl == 0 .OR. ghla_count == 0 ) THEN
+             ghla_count = 1
+          ELSE
+             ghla_empty = .FALSE.
+          ENDIF
+          IF ( nxr == nx .OR. ghra_count == 0 ) THEN
+             ghra_count = 1
+          ELSE
+             ghra_empty = .FALSE.
+          ENDIF
+          ALLOCATE( ghla(1:ghla_count), ghra(1:ghra_count) )
+          ghla = zero_agent
+          ghra = zero_agent
+!
+!--       Get all agents that will be sent left into one array
+          ghla_count = 0
+          IF ( nxl /= 0 ) THEN
+             DO ip = nxl, nxl+2
+                DO jp = nys, nyn
+                   number_of_agents = agt_count(jp,ip)
+                   IF ( number_of_agents <= 0 )  CYCLE
+                   ghla(ghla_count+1:ghla_count+number_of_agents)              &
+                       = grid_agents(jp,ip)%agents(1:number_of_agents)
+                   ghla_count = ghla_count + number_of_agents
+                ENDDO
+             ENDDO
+          ENDIF
+          IF ( ghla_count == 0 )  ghla_count = 1
+!
+!--       Get all agents that will be sent right into one array
+          ghra_count = 0
+          IF ( nxr /= nx ) THEN
+             DO ip = nxr-2, nxr
+                DO jp = nys, nyn
+                   number_of_agents = agt_count(jp,ip)
+                   IF ( number_of_agents <= 0 )  CYCLE
+                   ghra(ghra_count+1:ghra_count+number_of_agents)              &
+                       = grid_agents(jp,ip)%agents(1:number_of_agents)
+                   ghra_count = ghra_count + number_of_agents
+                ENDDO
+             ENDDO
+          ENDIF
+          IF ( ghra_count == 0 ) ghra_count = 1
+!
+!--       Send/receive number of agents that
+!--       will be transferred to/from left/right neighbor
+          CALL MPI_SENDRECV( ghla_count,      1, MPI_INTEGER, pleft,  0,       &
+                             ghra_count_recv, 1, MPI_INTEGER, pright, 0,       &
+                             comm2d, status, ierr )
+          ALLOCATE ( agt_gh_r(1:ghra_count_recv) )
+!
+!--       Send/receive number of agents that
+!--       will be transferred to/from right/left neighbor
+          CALL MPI_SENDRECV( ghra_count,      1, MPI_INTEGER, pright,  0,      &
+                             ghla_count_recv, 1, MPI_INTEGER, pleft,   0,      &
+                             comm2d, status, ierr )
+!
+!--       Send/receive flag that indicates if there are actually any agents
+!--       in ghost  layer
+          CALL MPI_SENDRECV( ghla_empty,     1, MPI_LOGICAL, pleft, 1,         &
+                             ghra_empty_rcv, 1, MPI_LOGICAL, pright,1,         &
+                             comm2d, status, ierr )
+          CALL MPI_SENDRECV( ghra_empty,     1, MPI_LOGICAL, pright,1,         &
+                             ghla_empty_rcv, 1, MPI_LOGICAL, pleft, 1,         &
+                             comm2d, status, ierr )
+          ALLOCATE ( agt_gh_l(1:ghla_count_recv) )
+!
+!--       Get bit size of one agent
+          agt_size = STORAGE_SIZE(zero_agent)/8
+!
+!--       Send/receive agents to/from left/right neighbor
+          CALL MPI_SENDRECV( ghla,     ghla_count      * agt_size, MPI_BYTE,   &
+                                pleft, 1,                                      &
+                             agt_gh_r, ghra_count_recv * agt_size, MPI_BYTE,   &
+                                pright,1,                                      &
+                             comm2d, status, ierr )
+!
+!--       Send/receive agents to/from left/right neighbor
+          CALL MPI_SENDRECV( ghra,     ghra_count      * agt_size, MPI_BYTE,   &
+                                pright,1,                                      &
+                             agt_gh_l, ghla_count_recv * agt_size, MPI_BYTE,   &
+                                pleft, 1,                                      &
+                             comm2d, status, ierr )
+!
+!--       If agents were received, add them to the respective ghost layer cells
+          IF ( .NOT. ghra_empty_rcv ) THEN
+             CALL mas_eh_add_ghost_agents_to_gridcell(agt_gh_r)
+          ENDIF
+          IF ( .NOT. ghla_empty_rcv ) THEN
+             CALL mas_eh_add_ghost_agents_to_gridcell(agt_gh_l)
+          ENDIF
+          DEALLOCATE( ghla, ghra, agt_gh_l, agt_gh_r )
+       ENDIF
+!
+!--    Transfer of agents from south to north and vice versa
+       IF ( pdims(2) /= 1 )  THEN
+!
+!--       Reset south and north ghost layers
+          ghsa_count  = 0
+          ghna_count  = 0
+!
+!--       First calculate the storage necessary for sending
+!--       and receiving the data.
+          ghsa_count = SUM(agt_count(nys:nys+2,nxlg:nxrg))
+          ghna_count = SUM(agt_count(nyn-2:nyn,nxlg:nxrg))
+!
+!--       No cyclic boundaries for agents
+          IF ( nys == 0 .OR. ghsa_count == 0 ) THEN
+             ghsa_count = 1
+          ELSE
+             ghsa_empty = .FALSE.
+          ENDIF
+          IF ( nyn == ny .OR. ghna_count == 0 ) THEN
+             ghna_count = 1
+          ELSE
+             ghna_empty = .FALSE.
+          ENDIF
+          ALLOCATE( ghsa(1:ghsa_count), ghna(1:ghna_count) )
+          ghsa = zero_agent
+          ghna = zero_agent
+!
+!--       Get all agents that will be sent south into one array
+          ghsa_count = 0
+          IF ( nys /= 0 ) THEN
+             DO ip = nxlg, nxrg
+                DO jp = nys, nys+2
+                   number_of_agents = agt_count(jp,ip)
+                   IF ( number_of_agents <= 0 )  CYCLE
+                   ghsa(ghsa_count+1:ghsa_count+number_of_agents)              &
+                       = grid_agents(jp,ip)%agents(1:number_of_agents)
+                   ghsa_count = ghsa_count + number_of_agents
+                ENDDO
+             ENDDO
+          ENDIF
+          IF ( ghsa_count == 0 )  ghsa_count = 1
+!
+!--       Get all agents that will be sent north into one array
+          ghna_count = 0
+          IF ( nyn /= ny ) THEN
+             DO ip = nxlg, nxrg
+                DO jp = nyn-2, nyn
+                   number_of_agents = agt_count(jp,ip)
+                   IF ( number_of_agents <= 0 )  CYCLE
+                   ghna(ghna_count+1:ghna_count+number_of_agents)              &
+                       = grid_agents(jp,ip)%agents(1:number_of_agents)
+                   ghna_count = ghna_count + number_of_agents
+                ENDDO
+             ENDDO
+          ENDIF
+          IF ( ghna_count == 0 ) ghna_count = 1
+!
+!--       Send/receive number of agents that
+!--       will be transferred to/from south/north neighbor
+          CALL MPI_SENDRECV( ghsa_count, 1, MPI_INTEGER, psouth, 0,            &
+                             ghna_count_recv,   1, MPI_INTEGER, pnorth, 0,     &
+                             comm2d, status, ierr )
+          ALLOCATE ( agt_gh_n(1:ghna_count_recv) )
+!
+!--       Send/receive number of agents that
+!--       will be transferred to/from north/south neighbor
+          CALL MPI_SENDRECV( ghna_count, 1, MPI_INTEGER, pnorth, 0,            &
+                             ghsa_count_recv,   1, MPI_INTEGER, psouth, 0,     &
+                             comm2d, status, ierr )
+!
+!--       Send/receive flag that indicates if there are actually any agents
+!--       in ghost  layer
+          CALL MPI_SENDRECV( ghsa_empty,     1, MPI_LOGICAL, psouth, 1,        &
+                             ghna_empty_rcv, 1, MPI_LOGICAL, pnorth, 1,        &
+                             comm2d, status, ierr )
+          CALL MPI_SENDRECV( ghna_empty,     1, MPI_LOGICAL, pnorth, 1,        &
+                             ghsa_empty_rcv, 1, MPI_LOGICAL, psouth, 1,        &
+                             comm2d, status, ierr )
+          ALLOCATE ( agt_gh_s(1:ghsa_count_recv) )
+!
+!--       Get bit size of one agent
+          agt_size = STORAGE_SIZE(zero_agent)/8
+!
+!--       Send/receive agents to/from south/north neighbor
+          CALL MPI_SENDRECV( ghsa,     ghsa_count      * agt_size, MPI_BYTE,   &
+                                psouth,1,                                      &
+                             agt_gh_n, ghna_count_recv * agt_size, MPI_BYTE,   &
+                                pnorth,1,                                      &
+                             comm2d, status, ierr )
+!
+!--       Send/receive agents to/from south/north neighbor
+          CALL MPI_SENDRECV( ghna,     ghna_count      * agt_size, MPI_BYTE,   &
+                                pnorth,1,                                      &
+                             agt_gh_s, ghsa_count_recv * agt_size, MPI_BYTE,   &
+                                psouth,1,                                      &
+                             comm2d, status, ierr )
+!
+!--       If agents were received, add them to the respective ghost layer cells
+          IF ( .NOT. ghna_empty_rcv ) THEN
+             CALL mas_eh_add_ghost_agents_to_gridcell(agt_gh_n)
+          ENDIF
+          IF ( .NOT. ghsa_empty_rcv ) THEN
+             CALL mas_eh_add_ghost_agents_to_gridcell(agt_gh_s)
+          ENDIF
+          DEALLOCATE( ghna, ghsa, agt_gh_n, agt_gh_s )
+       ENDIF
+    END SUBROUTINE mas_eh_ghost_exchange
+#endif
+!------------------------------------------------------------------------------!
+! Description:
+! ------------
+!> If an agent moves from one grid cell to another (on the current
+!> processor!), this subroutine moves the corresponding element from the
+!> agent array of the old grid cell to the agent array of the new grid
+!> cell.
+!------------------------------------------------------------------------------!
+    SUBROUTINE mas_eh_move_agent
+       IMPLICIT NONE
+       INTEGER(iwp) ::  i              !< grid index (x) of agent position
+       INTEGER(iwp) ::  ip             !< index variable along x
+       INTEGER(iwp) ::  j              !< grid index (y) of agent position
+       INTEGER(iwp) ::  jp             !< index variable along y
+       INTEGER(iwp) ::  n              !< index variable for agent array
+       INTEGER(iwp) ::  na_before_move !< number of agents per grid box before moving
+       INTEGER(iwp) ::  aindex         !< dummy argument for number of new agent per grid box
+       TYPE(agent_type), DIMENSION(:), POINTER ::  agents_before_move !< agents before moving
+       DO  ip = nxl, nxr
+          DO  jp = nys, nyn
+                na_before_move = agt_count(jp,ip)
+                IF ( na_before_move <= 0 )  CYCLE
+                agents_before_move => grid_agents(jp,ip)%agents(1:na_before_move)
+                DO  n = 1, na_before_move
+                   i = agents_before_move(n)%x * ddx
+                   j = agents_before_move(n)%y * ddy
+!--                For mas_eh_exchange_horiz to work properly agents need to be
+!--                moved to the outermost gridboxes of the respective processor.
+!--                If the agent index is inside the processor the following
+!--                lines will not change the index
+                   i = MIN ( i , nxr )
+                   i = MAX ( i , nxl )
+                   j = MIN ( j , nyn )
+                   j = MAX ( j , nys )
+!
+!--                Check if agent has moved to another grid cell.
+                   IF ( i /= ip  .OR.  j /= jp )  THEN
+!
+!--                   If the agent stays on the same processor, the agent
+!--                   will be added to the agent array of the new processor.
+                      number_of_agents = agt_count(j,i)
+                      agents => grid_agents(j,i)%agents(1:number_of_agents)
+                      aindex = number_of_agents+1
+                      IF (  aindex > SIZE(grid_agents(j,i)%agents)  )     &
+                      THEN
+                         CALL mas_eh_realloc_agents_array(i,j)
+                      ENDIF
+                      grid_agents(j,i)%agents(aindex) = agents_before_move(n)
+                      agt_count(j,i) = aindex
+                      agents_before_move(n)%agent_mask = .FALSE.
+                   ENDIF
+                ENDDO
+          ENDDO
+       ENDDO
+       RETURN
+    END SUBROUTINE mas_eh_move_agent
+!------------------------------------------------------------------------------!
+! Description:
+! ------------
+!> If the allocated memory for the agent array do not suffice to add arriving
+!> agents from neighbour grid cells, this subrouting reallocates the
+!> agent array to assure enough memory is available.
+!------------------------------------------------------------------------------!
+    SUBROUTINE mas_eh_realloc_agents_array (i,j,size_in)
+       IMPLICIT NONE
+       INTEGER(iwp) :: new_size  !< new array size
        INTEGER(iwp) :: old_size  !< old array size
-       INTEGER(iwp) :: new_size  !< new array size
        INTEGER(iwp), INTENT(in) ::  i  !< grid index (y)
 …
        INTEGER(iwp), INTENT(in), OPTIONAL ::  size_in  !< size of input array
        TYPE(agent_type), DIMENSION(10) :: tmp_agents_s !< temporary static agent array
        TYPE(agent_type), DIMENSION(:), ALLOCATABLE :: tmp_agents_d !< temporary dynamic agent array
+       TYPE(agent_type), DIMENSION(10) :: tmp_agents_s  !< temporary static agent array
+       TYPE(agent_type), DIMENSION(:), ALLOCATABLE :: tmp_agents_d  !< temporary dynamic agent array
        old_size = SIZE(grid_agents(j,i)%agents)
        IF ( PRESENT(size_in) )   THEN
+       IF ( PRESENT( size_in ) )  THEN
           new_size = size_in
        ELSE
 …
           tmp_agents_s(1:old_size) = grid_agents(j,i)%agents(1:old_size)
           DEALLOCATE(grid_agents(j,i)%agents)
           ALLOCATE(grid_agents(j,i)%agents(new_size))
+          DEALLOCATE( grid_agents(j,i)%agents )
+          ALLOCATE( grid_agents(j,i)%agents(new_size) )
           grid_agents(j,i)%agents(1:old_size)         = tmp_agents_s(1:old_size)
 …
        ELSE
           ALLOCATE(tmp_agents_d(new_size))
+          ALLOCATE( tmp_agents_d(new_size) )
           tmp_agents_d(1:old_size) = grid_agents(j,i)%agents
           DEALLOCATE(grid_agents(j,i)%agents)
           ALLOCATE(grid_agents(j,i)%agents(new_size))
+          DEALLOCATE( grid_agents(j,i)%agents )
+          ALLOCATE( grid_agents(j,i)%agents(new_size) )
           grid_agents(j,i)%agents(1:old_size)         = tmp_agents_d(1:old_size)
           grid_agents(j,i)%agents(old_size+1:new_size) = zero_agent
           DEALLOCATE(tmp_agents_d)
+          DEALLOCATE( tmp_agents_d )
        ENDIF
 …
     END SUBROUTINE mas_eh_realloc_agents_array
 !------------------------------------------------------------------------------!
+!--------------------------------------------------------------------------------------------------!
 ! Description:
 ! ------------
+!> Inquires prognostic model quantities at the position of each agent and
+!> stores them in that agent for later output
+!------------------------------------------------------------------------------!
+    SUBROUTINE mas_get_prognostic_quantities
+       USE arrays_3d,                                                          &
+           ONLY:  u, v, pt, exner
+       IMPLICIT NONE
+       INTEGER(iwp) ::  i_offset  !<  index offset for windspeed measurement
+       INTEGER(iwp) ::  il        !<  x-index
+       INTEGER(iwp) ::  is        !<  subgrid box counter
+       INTEGER(iwp) ::  j_offset  !<  index offset for windspeed measurement
+       INTEGER(iwp) ::  jl        !<  y-index
+       INTEGER(iwp) ::  kl        !<  z-index
+       INTEGER(iwp) ::  nl        !<  agent counter
+       INTEGER(iwp) ::  se        !<  subgrid box end index
+       INTEGER(iwp) ::  si        !<  subgrid box start index
+       REAL(wp) ::  u_a  !< windspeed at agent position (x)
+       REAL(wp) ::  v_a  !< windspeed at agent position (y)
+       DO  il = nxl, nxr
+          DO  jl = nys, nyn
+             number_of_agents = agt_count(jl,il)
+!
+!--          If grid cell is empty, cycle
+             IF ( number_of_agents <= 0 ) CYCLE
+             kl = s_measure_height(jl,il)
+             agents => grid_agents(jl,il)%agents(1:number_of_agents)
+!
+!--          loop over the four subgrid boxes
+             DO is = 0,3
+!
+!--             Set indices
+                si = grid_agents(jl,il)%start_index(is)
+                se = grid_agents(jl,il)%end_index(is)
+                DO nl = si, se
+!
+!--                Calculate index offset in x-direction:
+!--                Left value if wall right of grid box
+!--                Right value if wall left of grid box
+!--                Else the one that is closer to the agent
+                   IF ( BTEST( obstacle_flags( jl, il+1 ), 6 ) ) THEN
+                      i_offset = 0
+                   ELSEIF ( BTEST( obstacle_flags( jl, il-1 ), 2 ) ) THEN
+                      i_offset = 1
+                   ELSE
+                      i_offset = MERGE( 0, 1, BTEST(is,1) )
+                   ENDIF
+                   u_a = u( kl, jl, il + i_offset )
+!
+!--                Calculate index offset in y-direction:
+!--                South value if wall north of grid box
+!--                North value if wall south of grid box
+!--                Else the one that is closer to the agent
+                   IF ( BTEST( obstacle_flags( jl+1, il ), 4 ) ) THEN
+                      j_offset = 0
+                   ELSEIF ( BTEST( obstacle_flags( jl-1, il ), 0 ) ) THEN
+                      j_offset = 1
+                   ELSE
+                      j_offset = MERGE( 0, 1, BTEST(is,0) )
+                   ENDIF
+                   v_a = v( kl, jl + j_offset, il )
+!
+!--                Calculate windspeed at agent postion
+                   agents(nl)%windspeed = SQRT(u_a**2 + v_a**2)
+!
+!--                Calculate temperature at agent position
+                   agents(nl)%t = pt(kl,jl,il) * exner(kl)
+                ENDDO
+!> Inquires prognostic model quantities at the position of each agent and stores them in that agent
+!> for later output
+!--------------------------------------------------------------------------------------------------!
+ SUBROUTINE mas_get_prognostic_quantities
+    USE arrays_3d,                                                                                 &
+        ONLY:  exner, pt, u, v
+    IMPLICIT NONE
+    INTEGER(iwp) ::  i_offset  !<  index offset for windspeed measurement
+    INTEGER(iwp) ::  il        !<  x-index
+    INTEGER(iwp) ::  is        !<  subgrid box counter
+    INTEGER(iwp) ::  j_offset  !<  index offset for windspeed measurement
+    INTEGER(iwp) ::  jl        !<  y-index
+    INTEGER(iwp) ::  kl        !<  z-index
+    INTEGER(iwp) ::  nl        !<  agent counter
+    INTEGER(iwp) ::  se        !<  subgrid box end index
+    INTEGER(iwp) ::  si        !<  subgrid box start index
+    REAL(wp) ::  u_a  !< windspeed at agent position (x)
+    REAL(wp) ::  v_a  !< windspeed at agent position (y)
+    DO  il = nxl, nxr
+       DO  jl = nys, nyn
+          number_of_agents = agt_count(jl,il)
+!
+!--       If grid cell is empty, cycle
+          IF ( number_of_agents <= 0 )  CYCLE
+          kl = s_measure_height(jl,il)
+          agents => grid_agents(jl,il)%agents(1:number_of_agents)
+!
+!--       Loop over the four subgrid boxes
+          DO  is = 0,3
+!
+!--          Set indices
+             si = grid_agents(jl,il)%start_index(is)
+             se = grid_agents(jl,il)%end_index(is)
+             DO  nl = si, se
+!
+!--             Calculate index offset in x-direction:
+!--             Left value if wall right of grid box
+!--             Right value if wall left of grid box
+!--             Else the one that is closer to the agent
+                IF ( BTEST( obstacle_flags( jl, il+1 ), 6 ) )  THEN
+                   i_offset = 0
+                ELSEIF ( BTEST( obstacle_flags( jl, il-1 ), 2 ) )  THEN
+                   i_offset = 1
+                ELSE
+                   i_offset = MERGE( 0, 1, BTEST(is,1) )
+                ENDIF
+                u_a = u( kl, jl, il + i_offset )
+!
+!--             Calculate index offset in y-direction:
+!--             South value if wall north of grid box
+!--             North value if wall south of grid box
+!--             Else the one that is closer to the agent
+                IF ( BTEST( obstacle_flags( jl+1, il ), 4 ) )  THEN
+                   j_offset = 0
+                ELSEIF ( BTEST( obstacle_flags( jl-1, il ), 0 ) )  THEN
+                   j_offset = 1
+                ELSE
+                   j_offset = MERGE( 0, 1, BTEST(is,0) )
+                ENDIF
+                v_a = v( kl, jl + j_offset, il )
+!
+!--             Calculate windspeed at agent postion
+                agents(nl)%windspeed = SQRT(u_a**2 + v_a**2)
+!
+!--             Calculate temperature at agent position
+                agents(nl)%t = pt(kl,jl,il) * exner(kl)
              ENDDO
           ENDDO
        ENDDO
+    END SUBROUTINE mas_get_prognostic_quantities
+!------------------------------------------------------------------------------!
+    ENDDO
+ END SUBROUTINE mas_get_prognostic_quantities
+!--------------------------------------------------------------------------------------------------!
 ! Description:
 ! ------------
 !> Adds an item to the priority queue (binary heap) at the correct position
 !------------------------------------------------------------------------------!
     SUBROUTINE mas_heap_insert_item( id, priority )
        IMPLICIT NONE
        INTEGER(iwp) ::  cur_pos !< current position
        INTEGER(iwp) ::  id      !< mesh ID of item
        REAL(wp) ::  priority !< item priority
        TYPE(heap_item) ::  item !< heap item
        item%mesh_id  = id
        item%priority = priority
+!--------------------------------------------------------------------------------------------------!
+ SUBROUTINE mas_heap_insert_item( id, priority )
+    IMPLICIT NONE
+    INTEGER(iwp) ::  cur_pos  !< current position
+    INTEGER(iwp) ::  id       !< mesh ID of item
+    REAL(wp) ::  priority  !< item priority
+    TYPE(heap_item) ::  item  !< heap item
+    item%mesh_id  = id
+    item%priority = priority
+!
 !--    Extend heap, if necessary
+       IF ( heap_count + 1 > SIZE(queue) ) THEN
+          CALL mas_heap_extend
+    IF ( heap_count + 1 > SIZE( queue ) )  THEN
+       CALL mas_heap_extend
+    ENDIF
+!
+!-- Insert item at first unoccupied postion (highest index) of heap
+    cur_pos = heap_count
+    queue(cur_pos) = item
+!
+!-- Sort while inserted item is not at top of heap
+    DO WHILE ( cur_pos /= 0 )
+!
+!--    If priority < its parent's priority, swap them.
+!--    Else, sorting is done.
+       IF ( queue(cur_pos)%priority < queue(FLOOR( (cur_pos) / 2.0_wp ))%priority )  THEN
+          item = queue(cur_pos)
+          queue(cur_pos) = queue(FLOOR( ( cur_pos ) / 2.0_wp ))
+          queue(FLOOR( ( cur_pos ) / 2.0_wp )) = item
+          cur_pos = FLOOR( ( cur_pos ) / 2.0_wp )
+       ELSE
+          EXIT
        ENDIF
+!
+!--    Insert item at first unoccupied postion (highest index) of heap
+       cur_pos = heap_count
+       queue(cur_pos) = item
+!
+!--    Sort while inserted item is not at top of heap
+       DO WHILE ( cur_pos /= 0 )
+!
+!--       If priority < its parent's priority, swap them.
+!--       Else, sorting is done.
+          IF ( queue(cur_pos)%priority                                         &
+              < queue(FLOOR((cur_pos)/2.))%priority )                          &
+          THEN
+             item = queue(cur_pos)
+             queue(cur_pos) = queue(FLOOR((cur_pos)/2.))
+             queue(FLOOR((cur_pos)/2.)) = item
+             cur_pos = FLOOR((cur_pos)/2.)
+    ENDDO
+!
+!-- Item was added to heap, so the heap count increases
+    heap_count = heap_count + 1
+ END SUBROUTINE mas_heap_insert_item
+!--------------------------------------------------------------------------------------------------!
+! Description:
+! ------------
+!> Extends the size of the priority queue (binary heap)
+!--------------------------------------------------------------------------------------------------!
+ SUBROUTINE mas_heap_extend
+    IMPLICIT NONE
+    INTEGER(iwp) ::  soh  !< size of heap
+    TYPE(heap_item), DIMENSION(:), ALLOCATABLE ::  dummy_heap  !< dummy heap
+    soh = SIZE( queue ) - 1
+    ALLOCATE( dummy_heap(0:soh) )
+    dummy_heap = queue
+    DEALLOCATE( queue )
+    ALLOCATE( queue(0:2*soh+1) )
+    queue(0:soh) = dummy_heap(0:soh)
+ END SUBROUTINE mas_heap_extend
+!--------------------------------------------------------------------------------------------------!
+! Description:
+! ------------
+!> Removes first (smallest) element from the priority queue, reorders the rest and returns the ID of
+!> the removed mesh point
+!--------------------------------------------------------------------------------------------------!
+ SUBROUTINE mas_heap_extract_item ( id )
+    IMPLICIT NONE
+    INTEGER(iwp) ::  child    !< child of item in heap
+    INTEGER(iwp) ::  cur_pos  !< current position of item in heap
+    INTEGER(iwp) ::  id       !< ID of item extracted item
+    TYPE(heap_item) ::  dummy
+!
+!-- Get ID of mesh point with lowest priority (extracted item: top of heap)
+    id = queue(0)%mesh_id
+!
+!-- Put last item in heap at first position
+    queue(0) = queue(heap_count-1)
+    cur_pos = 0
+    DO
+!
+!--    If current item has no children, sorting is done
+       IF( 2*cur_pos+1 > heap_count - 1 )  THEN
+          EXIT
+!
+!--    If current item has only one child, check if item and its child are ordered correctly. Else,
+!--    swap them.
+       ELSEIF ( 2*cur_pos+2 > heap_count - 1 )  THEN
+          IF ( queue(cur_pos)%priority > queue(2*cur_pos+1)%priority )  THEN
+             dummy = queue(cur_pos)
+             queue(cur_pos) = queue(2*cur_pos+1)
+             queue(2*cur_pos+1) = dummy
+             cur_pos = 2*cur_pos+1
           ELSE
              EXIT
           ENDIF
+       ENDDO
+!
+!--    Item was added to heap, so the heap count increases
+       heap_count = heap_count + 1
+    END SUBROUTINE mas_heap_insert_item
+!------------------------------------------------------------------------------!
+! Description:
+! ------------
+!> Extends the size of the priority queue (binary heap)
+!------------------------------------------------------------------------------!
+    SUBROUTINE mas_heap_extend
+       IMPLICIT NONE
+       INTEGER(iwp) ::  soh !< size of heap
+       TYPE(heap_item), DIMENSION(:), ALLOCATABLE ::  dummy_heap !< dummy heap
+       soh = SIZE(queue)-1
+       ALLOCATE(dummy_heap(0:soh))
+       dummy_heap = queue
+       DEALLOCATE(queue)
+       ALLOCATE(queue(0:2*soh+1))
+       queue(0:soh) = dummy_heap(0:soh)
+    END SUBROUTINE mas_heap_extend
+!------------------------------------------------------------------------------!
+! Description:
+! ------------
+!> Removes first (smallest) element from the priority queue, reorders the rest
+!> and returns the ID of the removed mesh point
+!------------------------------------------------------------------------------!
+    SUBROUTINE mas_heap_extract_item ( id )
+       IMPLICIT NONE
+       INTEGER(iwp) ::  id      !< ID of item extracted item
+       INTEGER(iwp) ::  child   !< child of item in heap
+       INTEGER(iwp) ::  cur_pos !< current position of item in heap
+       TYPE(heap_item) ::  dummy
+!
+!--    Get ID of mesh point with lowest priority (extracted item: top of heap)
+       id = queue(0)%mesh_id
+!
+!--    Put last item in heap at first position
+       queue(0) = queue(heap_count-1)
+       cur_pos = 0
+       DO
+!
+!--       If current item has no children, sorting is done
+          IF( 2*cur_pos+1 > heap_count - 1 ) THEN
+       ELSE
+!
+!--       Determine the smaller child
+          IF ( queue(2*cur_pos+1)%priority >= queue(2*cur_pos+2)%priority )  THEN
+             child = 2
+          ELSE
+             child = 1
+          ENDIF
+!
+!--       Check if item and its smaller child are ordered falsely. If so, swap them. Else, sorting
+!--       is done.
+          IF ( queue(cur_pos)%priority > queue(2*cur_pos+child )%priority )  THEN
+             dummy = queue(cur_pos)
+             queue(cur_pos) = queue(2*cur_pos+child)
+             queue(2*cur_pos+child) = dummy
+             cur_pos = 2*cur_pos+child
+          ELSE
              EXIT
+!
-!--       If current item has only one child, check if item and its child are
-!--       ordered correctly. Else, swap them.
-          ELSEIF ( 2*cur_pos+2 > heap_count - 1 ) THEN
-             IF ( queue(cur_pos)%priority > queue(2*cur_pos+1)%priority ) THEN
-                dummy = queue(cur_pos)
-                queue(cur_pos) = queue(2*cur_pos+1)
-                queue(2*cur_pos+1) = dummy
-                cur_pos = 2*cur_pos+1
-             ELSE
-                EXIT
-             ENDIF
-          ELSE
+!
-!--          determine the smaller child
-             IF ( queue(2*cur_pos+1)%priority                                  &
-                 >= queue(2*cur_pos+2)%priority )                              &
-             THEN
-                child = 2
-             ELSE
-                child = 1
-             ENDIF
+!
-!--          Check if item and its smaller child are ordered falsely. If so,
-!--          swap them. Else, sorting is done.
-             IF ( queue(cur_pos)%priority > queue(2*cur_pos+child )%priority ) &
-             THEN
-                dummy = queue(cur_pos)
-                queue(cur_pos) = queue(2*cur_pos+child)
-                queue(2*cur_pos+child) = dummy
-                cur_pos = 2*cur_pos+child
-             ELSE
-                EXIT
-             ENDIF
           ENDIF
+       ENDDO
+!
+!--    Top item was removed from heap, thus, heap_cout decreases by one
+       heap_count = heap_count-1
+    END SUBROUTINE mas_heap_extract_item
+!------------------------------------------------------------------------------!
+       ENDIF
+    ENDDO
+!
+!-- Top item was removed from heap, thus, heap_cout decreases by one
+    heap_count = heap_count-1
+ END SUBROUTINE mas_heap_extract_item
+!--------------------------------------------------------------------------------------------------!
 ! Description:
 ! ------------
 !> Initialization of Multi Agent System
+!------------------------------------------------------------------------------!
+    SUBROUTINE mas_init
+       USE control_parameters,                                                 &
+           ONLY:  coupling_char, initializing_actions, io_blocks, io_group
+       USE arrays_3d,                                                          &
+           ONLY:  zu, zw
+       USE indices,                                                            &
+           ONLY:  nzt
+       IMPLICIT NONE
+       INTEGER(iwp) ::  i             !< grid cell (x)
+       INTEGER(iwp) ::  ii            !< io-block counter
+       INTEGER(iwp) ::  il            !< io-block counter
+       INTEGER(iwp) ::  jl            !< io-block counter
+       INTEGER(iwp) ::  kl            !< io-block counter
+       INTEGER(iwp) ::  kdum            !< io-block counter
+       INTEGER(iwp) ::  locdum            !< io-block counter
+       INTEGER(iwp) ::  j             !< grid cell (y)
+       INTEGER(iwp) ::  size_of_mesh  !< temporary value for read
+       INTEGER(iwp) ::  size_of_pols  !< temporary value for read
+       INTEGER(iwp) ::  ioerr         !< IOSTAT flag for IO-commands ( 0 = no error )
+       LOGICAL ::  navigation_data_present  !< Flag: check for input file
+       REAL(wp) ::  zdum  !< dummy for measurement height
+       REAL(wp) ::  avg_agt_height = 1.8_wp
+!
+!--    Check the number of agent groups.
+       IF ( number_of_agent_groups > max_number_of_agent_groups )  THEN
+          WRITE( message_string, * ) 'max_number_of_agent_groups =',      &
+                                     max_number_of_agent_groups ,         &
+                                     '&number_of_agent_groups reset to ', &
+                                     max_number_of_agent_groups
+          CALL message( 'mas_init', 'PA0072', 0, 1, 0, 6, 0 )
+          number_of_agent_groups = max_number_of_agent_groups
+       ENDIF
+!
+!--    Set some parameters
+       d_sigma_rep_agent = 1.0_wp/sigma_rep_agent
+       d_sigma_rep_wall  = 1.0_wp/sigma_rep_wall
+       d_tau_accel_agent = 1.0_wp/tau_accel_agent
+       IF ( dt_agent /= 999.0_wp ) THEN
+          agent_own_timestep = .TRUE.
+       ENDIF
+!
+!--    Get index of first grid box above topography
+       ALLOCATE( top_top_s(nysg:nyng,nxlg:nxrg),                               &
+                 top_top_w(nysg:nyng,nxlg:nxrg),                               &
+                 s_measure_height(nys:nyn,nxl:nxr) )
+!
+!--    Get first index above topography for scalar grid and last index in
+!--    topography for z-component of wind
+       DO il = nxlg, nxrg
+          DO jl = nysg, nyng
+             top_top_s(jl,il) = topo_top_ind(jl,il,0) + 1
+             top_top_w(jl,il) = topo_top_ind(jl,il,3)
+!--------------------------------------------------------------------------------------------------!
+ SUBROUTINE mas_init
+    USE control_parameters,                                                                        &
+        ONLY:  coupling_char, initializing_actions, io_blocks, io_group
+    USE arrays_3d,                                                                                 &
+        ONLY:  zu, zw
+    USE indices,                                                                                   &
+        ONLY:  nzt
+    IMPLICIT NONE
+    INTEGER(iwp) ::  i             !< grid cell (x)
+    INTEGER(iwp) ::  ii            !< io-block counter
+    INTEGER(iwp) ::  il            !< io-block counter
+    INTEGER(iwp) ::  ioerr         !< IOSTAT flag for IO-commands ( 0 = no error )
+    INTEGER(iwp) ::  j             !< grid cell (y)
+    INTEGER(iwp) ::  jl            !< io-block counter
+    INTEGER(iwp) ::  kl            !< io-block counter
+    INTEGER(iwp) ::  kdum          !< io-block counter
+    INTEGER(iwp) ::  locdum        !< io-block counter
+    INTEGER(iwp) ::  size_of_mesh  !< temporary value for read
+    INTEGER(iwp) ::  size_of_pols  !< temporary value for read
+    LOGICAL ::  navigation_data_present  !< Flag: check for input file
+    REAL(wp) ::  zdum  !< dummy for measurement height
+    REAL(wp) ::  avg_agt_height = 1.8_wp
+!
+!-- Check the number of agent groups.
+    IF ( number_of_agent_groups > max_number_of_agent_groups )  THEN
+       WRITE( message_string, * ) 'max_number_of_agent_groups =', max_number_of_agent_groups ,     &
+                                  '&number_of_agent_groups reset to ', max_number_of_agent_groups
+       CALL message( 'mas_init', 'PA0072', 0, 1, 0, 6, 0 )
+       number_of_agent_groups = max_number_of_agent_groups
+    ENDIF
+!
+!-- Set some parameters
+    d_sigma_rep_agent = 1.0_wp/sigma_rep_agent
+    d_sigma_rep_wall  = 1.0_wp/sigma_rep_wall
+    d_tau_accel_agent = 1.0_wp/tau_accel_agent
+    IF ( dt_agent /= 999.0_wp )  THEN
+       agent_own_timestep = .TRUE.
+    ENDIF
+!
+!-- Get index of first grid box above topography
+    ALLOCATE( top_top_s(nysg:nyng,nxlg:nxrg),                                                      &
+              top_top_w(nysg:nyng,nxlg:nxrg),                                                      &
+              s_measure_height(nys:nyn,nxl:nxr) )
+!
+!-- Get first index above topography for scalar grid and last index in topography for z-component of
+!-- wind.
+    DO  il = nxlg, nxrg
+       DO  jl = nysg, nyng
+          top_top_s(jl,il) = topo_top_ind(jl,il,0) + 1
+          top_top_w(jl,il) = topo_top_ind(jl,il,3)
+       ENDDO
+    ENDDO
+!
+!-- Create 2D array containing the index at which measurements are done by agents. The height of
+!-- this measurement is given by avg_agt_height.
+    DO  il = nxl, nxr
+       DO  jl = nys, nyn
+          kdum = top_top_w(jl,il)
+          zdum = zw(kdum)
+          zdum = zdum + avg_agt_height
+          locdum = 0
+!
+!--       Locate minimum distance from u-grid to measurement height (zdum)
+          DO  kl = 1, nzt
+             IF ( ABS(zu(kl)-zdum) < ABS(zu(locdum)-zdum) ) locdum = kl
           ENDDO
+          s_measure_height(jl,il) = locdum
        ENDDO
+!
+!--    Create 2D array containing the index at which measurements are done by
+!--    agents. The height of this measurement is given by avg_agt_height.
+       DO il = nxl, nxr
+          DO jl = nys, nyn
+             kdum = top_top_w(jl,il)
+             zdum = zw(kdum)
+             zdum = zdum + avg_agt_height
+             locdum = 0
+!
+!--          Locate minimum distance from u-grid to measurement height (zdum)
+             DO kl = 1, nzt
+                IF ( ABS(zu(kl)-zdum) < ABS(zu(locdum)-zdum) ) locdum = kl
+    ENDDO
+    CALL mas_create_obstacle_flags
+!
+!-- Set default start positions, if necessary
+    IF ( asl(1) == 9999999.9_wp )  asl(1) = 0.0_wp
+    IF ( asr(1) == 9999999.9_wp )  asr(1) = ( nx + 1 ) * dx
+    IF ( ass(1) == 9999999.9_wp )  ass(1) = 0.0_wp
+    IF ( asn(1) == 9999999.9_wp )  asn(1) = ( ny + 1 ) * dy
+    IF ( adx(1) == 9999999.9_wp  .OR.  adx(1) == 0.0_wp ) adx(1) = dx
+    IF ( ady(1) == 9999999.9_wp  .OR.  ady(1) == 0.0_wp ) ady(1) = dy
+    DO  j = 2, number_of_agent_groups
+       IF ( asl(j) == 9999999.9_wp )  asl(j) = asl(j-1)
+       IF ( asr(j) == 9999999.9_wp )  asr(j) = asr(j-1)
+       IF ( ass(j) == 9999999.9_wp )  ass(j) = ass(j-1)
+       IF ( asn(j) == 9999999.9_wp )  asn(j) = asn(j-1)
+       IF ( adx(j) == 9999999.9_wp  .OR.  adx(j) == 0.0_wp ) adx(j) = adx(j-1)
+       IF ( ady(j) == 9999999.9_wp  .OR.  ady(j) == 0.0_wp ) ady(j) = ady(j-1)
+    ENDDO
+!
+!-- Check boundary condition and set internal variables
+    SELECT CASE ( bc_mas_lr )
+       CASE ( 'cyclic' )
+          ibc_mas_lr = 0
+       CASE ( 'absorb' )
+          ibc_mas_lr = 1
+       CASE DEFAULT
+          WRITE( message_string, * ) 'unknown boundary condition ',                                &
+                                     'bc_mas_lr = "', TRIM( bc_mas_lr ), '"'
+          CALL message( 'mas_init', 'PA0073', 1, 2, 0, 6, 0 )
+    END SELECT
+    SELECT CASE ( bc_mas_ns )
+       CASE ( 'cyclic' )
+          ibc_mas_ns = 0
+       CASE ( 'absorb' )
+          ibc_mas_ns = 1
+       CASE DEFAULT
+          WRITE( message_string, * ) 'unknown boundary condition ',                                &
+                                     'bc_mas_ns = "', TRIM( bc_mas_ns ), '"'
+          CALL message( 'mas_init', 'PA0074', 1, 2, 0, 6, 0 )
+    END SELECT
+!
+!-- For the first model run of a possible job chain initialize the agents, otherwise read the agent
+!-- data from restart file.
+    IF ( TRIM( initializing_actions ) == 'read_restart_data'  .AND.  read_agents_from_restartfile )&
+    THEN
+!           CALL mas_read_restart_file
+    ELSE
+!
+!--    Read preprocessed data of navigation mesh and building polygons for agent pathfinding
+       DO  ii = 0, io_blocks-1
+          IF ( ii == io_group )  THEN
+!
+!--          Check for naviation input file and open it
+             INQUIRE( FILE='NAVIGATION_DATA' // TRIM( coupling_char ),                             &
+                      EXIST=navigation_data_present )
+             IF ( .NOT. navigation_data_present )  THEN
+                message_string = 'Input file NAVIGATION_DATA' //                                   &
+                                  TRIM( coupling_char ) // ' for MAS missing. ' //                 &
+                                  '&Please run agent_preprocessing before the job to create it.'
+                CALL message( 'mas_init', 'PA0525', 1, 2, 0, 6, 0 )
+             ENDIF
+             OPEN ( 119, FILE='NAVIGATION_DATA'//TRIM( coupling_char ), FORM='UNFORMATTED',        &
+                         IOSTAT=ioerr )
+!
+!--             Read mesh data
+             READ( 119 ) size_of_mesh
+             ALLOCATE( mesh(1:size_of_mesh) )
+             DO  i = 1, size_of_mesh
+                READ( 119 ) mesh(i)%polygon_id, mesh(i)%vertex_id,                                 &
+                            mesh(i)%noc, mesh(i)%origin_id,                                        &
+                            mesh(i)%cost_so_far, mesh(i)%x,                                        &
+                            mesh(i)%y, mesh(i)%x_s, mesh(i)%y_s
+                ALLOCATE( mesh(i)%connected_vertices(1:mesh(i)%noc),                               &
+                          mesh(i)%distance_to_vertex(1:mesh(i)%noc) )
+                DO  j = 1, mesh(i)%noc
+                   READ( 119 ) mesh(i)%connected_vertices(j),                                      &
+                               mesh(i)%distance_to_vertex(j)
+                ENDDO
              ENDDO
+             s_measure_height(jl,il) = locdum
+          ENDDO
+!
+!--             Read polygon data
+             READ( 119 ) size_of_pols
+             ALLOCATE( polygons(1:size_of_pols) )
+             DO  i = 1, size_of_pols
+                READ( 119 ) polygons(i)%nov
+                ALLOCATE( polygons(i)%vertices(0:polygons(i)%nov+1) )
+                DO  j = 0, polygons(i)%nov+1
+                   READ( 119 ) polygons(i)%vertices(j)%delete,                                     &
+                               polygons(i)%vertices(j)%x,                                          &
+                               polygons(i)%vertices(j)%y
+                ENDDO
+             ENDDO
+             CLOSE(119)
+          ENDIF
+#if defined( __parallel ) && ! defined ( __check )
+          CALL MPI_BARRIER( comm2d, ierr )
+#endif
        ENDDO
+       CALL mas_create_obstacle_flags
+!
+!--    Set default start positions, if necessary
+       IF ( asl(1) == 9999999.9_wp )  asl(1) = 0.0_wp
+       IF ( asr(1) == 9999999.9_wp )  asr(1) = ( nx + 1 ) * dx
+       IF ( ass(1) == 9999999.9_wp )  ass(1) = 0.0_wp
+       IF ( asn(1) == 9999999.9_wp )  asn(1) = ( ny + 1 ) * dy
+       IF ( adx(1) == 9999999.9_wp .OR. adx(1) == 0.0_wp ) adx(1) = dx
+       IF ( ady(1) == 9999999.9_wp .OR. ady(1) == 0.0_wp ) ady(1) = dy
+       DO  j = 2, number_of_agent_groups
+          IF ( asl(j) == 9999999.9_wp )  asl(j) = asl(j-1)
+          IF ( asr(j) == 9999999.9_wp )  asr(j) = asr(j-1)
+          IF ( ass(j) == 9999999.9_wp )  ass(j) = ass(j-1)
+          IF ( asn(j) == 9999999.9_wp )  asn(j) = asn(j-1)
+          IF ( adx(j) == 9999999.9_wp .OR. adx(j) == 0.0_wp ) adx(j) = adx(j-1)
+          IF ( ady(j) == 9999999.9_wp .OR. ady(j) == 0.0_wp ) ady(j) = ady(j-1)
+       ENDDO
+!
+!--    Check boundary condition and set internal variables
+       SELECT CASE ( bc_mas_lr )
+          CASE ( 'cyclic' )
+             ibc_mas_lr = 0
+          CASE ( 'absorb' )
+             ibc_mas_lr = 1
+          CASE DEFAULT
+             WRITE( message_string, * ) 'unknown boundary condition ',         &
+                                        'bc_mas_lr = "', TRIM( bc_mas_lr ), '"'
+             CALL message( 'mas_init', 'PA0073', 1, 2, 0, 6, 0 )
+       END SELECT
+       SELECT CASE ( bc_mas_ns )
+          CASE ( 'cyclic' )
+             ibc_mas_ns = 0
+          CASE ( 'absorb' )
+             ibc_mas_ns = 1
+          CASE DEFAULT
+             WRITE( message_string, * ) 'unknown boundary condition ',         &
+                                        'bc_mas_ns = "', TRIM( bc_mas_ns ), '"'
+             CALL message( 'mas_init', 'PA0074', 1, 2, 0, 6, 0 )
+       END SELECT
+!
+!--    For the first model run of a possible job chain initialize the
+!--    agents, otherwise read the agent data from restart file.
+       IF ( TRIM( initializing_actions ) == 'read_restart_data'                &
+            .AND.  read_agents_from_restartfile )  THEN
+!           CALL mas_read_restart_file
+       ELSE
+!
+!--       Read preprocessed data of navigation mesh and building polygons
+!--       for agent pathfinding
+          DO ii = 0, io_blocks-1
+             IF ( ii == io_group )  THEN
+!
+!--             Check for naviation input file and open it
+                INQUIRE( FILE='NAVIGATION_DATA' // TRIM( coupling_char ), EXIST=navigation_data_present )
+                IF ( .NOT. navigation_data_present )  THEN
+                   message_string = 'Input file NAVIGATION_DATA' //                &
+                                     TRIM( coupling_char ) // ' for MAS missing. ' // &
+                                     '&Please run agent_preprocessing before the job to create it.'
+                   CALL message( 'mas_init', 'PA0525', 1, 2, 0, 6, 0 )
+                ENDIF
+                OPEN ( 119, FILE='NAVIGATION_DATA'//TRIM( coupling_char ),     &
+                            FORM='UNFORMATTED', IOSTAT=ioerr )
+!
+!--             Read mesh data
+                READ(119) size_of_mesh
+                ALLOCATE( mesh(1:size_of_mesh))
+                DO i = 1, size_of_mesh
+                   READ(119) mesh(i)%polygon_id, mesh(i)%vertex_id,            &
+                             mesh(i)%noc, mesh(i)%origin_id,                   &
+                             mesh(i)%cost_so_far, mesh(i)%x,                   &
+                             mesh(i)%y, mesh(i)%x_s, mesh(i)%y_s
+                   ALLOCATE( mesh(i)%connected_vertices(1:mesh(i)%noc),        &
+                             mesh(i)%distance_to_vertex(1:mesh(i)%noc) )
+                   DO j = 1, mesh(i)%noc
+                      READ(119) mesh(i)%connected_vertices(j),                 &
+                                mesh(i)%distance_to_vertex(j)
+                   ENDDO
+                ENDDO
+!
+!--             Read polygon data
+                READ(119) size_of_pols
+                ALLOCATE( polygons(1:size_of_pols) )
+                DO i = 1, size_of_pols
+                   READ(119) polygons(i)%nov
+                   ALLOCATE( polygons(i)%vertices(0:polygons(i)%nov+1) )
+                   DO j = 0, polygons(i)%nov+1
+                      READ(119) polygons(i)%vertices(j)%delete,                &
+                                polygons(i)%vertices(j)%x,                     &
+                                polygons(i)%vertices(j)%y
+                   ENDDO
+                ENDDO
+                CLOSE(119)
+             ENDIF
+#if defined( __parallel ) && ! defined ( __check )
+             CALL MPI_BARRIER( comm2d, ierr )
+#endif
+          ENDDO
+!
+!--       Allocate agent arrays and set attributes of the initial set of
+!--       agents, which can be also periodically released at later times.
+          ALLOCATE( agt_count  (nysg:nyng,nxlg:nxrg),                          &
+                    grid_agents(nysg:nyng,nxlg:nxrg) )
+!
+!--       Allocate dummy arrays for pathfinding
+          ALLOCATE( dummy_path_x(0:agt_path_size),                 &
+                    dummy_path_y(0:agt_path_size) )
+          number_of_agents = 0
+          sort_count_mas   = 0
+          agt_count        = 0
+!
+!--       initialize counter for agent IDs
+          grid_agents%id_counter = 1
+!
+!--       Initialize all agents with dummy values (otherwise errors may
+!--       occur within restart runs). The reason for this is still not clear
+!--       and may be presumably caused by errors in the respective user-interface.
+          zero_agent%agent_mask = .FALSE.
+          zero_agent%block_nr      = -1
+          zero_agent%group         = 0
+          zero_agent%id            = 0_idp
+          zero_agent%path_counter  = agt_path_size
+          zero_agent%age           = 0.0_wp
+          zero_agent%age_m         = 0.0_wp
+          zero_agent%dt_sum        = 0.0_wp
+          zero_agent%clo           = 0.0_wp
+          zero_agent%energy_storage= 0.0_wp
+          zero_agent%force_x       = 0.0_wp
+          zero_agent%force_y       = 0.0_wp
+          zero_agent%origin_x      = 0.0_wp
+          zero_agent%origin_y      = 0.0_wp
+          zero_agent%speed_abs     = 0.0_wp
+          zero_agent%speed_e_x     = 0.0_wp
+          zero_agent%speed_e_y     = 0.0_wp
+          zero_agent%speed_des     = random_normal(desired_speed, des_sp_sig)
+          zero_agent%speed_x       = 0.0_wp
+          zero_agent%speed_y       = 0.0_wp
+          zero_agent%ipt           = 0.0_wp
+          zero_agent%x             = 0.0_wp
+          zero_agent%y             = 0.0_wp
+          zero_agent%path_x        = 0.0_wp
+          zero_agent%path_y        = 0.0_wp
+          zero_agent%t_x           = 0.0_wp
+          zero_agent%t_y           = 0.0_wp
+!
+!--    Set a seed value for the random number generator to be exclusively
+!--    used for the agent code. The generated random numbers should be
+!--    different on the different PEs.
+          iran_agent = iran_agent + myid
+          CALL mas_create_agent (PHASE_INIT)
+       ENDIF
+!
+!--    To avoid programm abort, assign agents array to the local version of
+!--    first grid cell
+       number_of_agents = agt_count(nys,nxl)
+       agents => grid_agents(nys,nxl)%agents(1:number_of_agents)
+    END SUBROUTINE mas_init
+!------------------------------------------------------------------------------!
+!
+!--    Allocate agent arrays and set attributes of the initial set of agents, which can be also
+!--    periodically released at later times.
+       ALLOCATE( agt_count  (nysg:nyng,nxlg:nxrg),                                                 &
+                 grid_agents(nysg:nyng,nxlg:nxrg) )
+!
+!--    Allocate dummy arrays for pathfinding
+       ALLOCATE( dummy_path_x(0:agt_path_size),                                                    &
+                 dummy_path_y(0:agt_path_size) )
+       number_of_agents = 0
+       sort_count_mas   = 0
+       agt_count        = 0
+!
+!--    Initialize counter for agent IDs
+       grid_agents%id_counter = 1
+!
+!--    Initialize all agents with dummy values (otherwise errors may occur within restart runs).
+!--    The reason for this is still not clear and may be presumably caused by errors in the
+!--    respective user-interface.
+       zero_agent%agent_mask = .FALSE.
+       zero_agent%block_nr      = -1
+       zero_agent%group         = 0
+       zero_agent%id            = 0_idp
+       zero_agent%path_counter  = agt_path_size
+       zero_agent%age           = 0.0_wp
+       zero_agent%age_m         = 0.0_wp
+       zero_agent%dt_sum        = 0.0_wp
+       zero_agent%clo           = 0.0_wp
+       zero_agent%energy_storage= 0.0_wp
+       zero_agent%force_x       = 0.0_wp
+       zero_agent%force_y       = 0.0_wp
+       zero_agent%origin_x      = 0.0_wp
+       zero_agent%origin_y      = 0.0_wp
+       zero_agent%speed_abs     = 0.0_wp
+       zero_agent%speed_e_x     = 0.0_wp
+       zero_agent%speed_e_y     = 0.0_wp
+       zero_agent%speed_des     = random_normal(desired_speed, des_sp_sig)
+       zero_agent%speed_x       = 0.0_wp
+       zero_agent%speed_y       = 0.0_wp
+       zero_agent%ipt           = 0.0_wp
+       zero_agent%x             = 0.0_wp
+       zero_agent%y             = 0.0_wp
+       zero_agent%path_x        = 0.0_wp
+       zero_agent%path_y        = 0.0_wp
+       zero_agent%t_x           = 0.0_wp
+       zero_agent%t_y           = 0.0_wp
+!
+!--    Set a seed value for the random number generator to be exclusively used for the agent code.
+!--    The generated random numbers should be different on the different PEs.
+       iran_agent = iran_agent + myid
+       CALL mas_create_agent( phase_init )
+    ENDIF
+!
+!-- To avoid programm abort, assign agents array to the local version of first grid cell.
+    number_of_agents = agt_count(nys,nxl)
+    agents => grid_agents(nys,nxl)%agents(1:number_of_agents)
+ END SUBROUTINE mas_init
+!--------------------------------------------------------------------------------------------------!
 ! Description:
 ! ------------
 !> Output of informative message about maximum agent number
+!------------------------------------------------------------------------------!
+    SUBROUTINE mas_last_actions
+       USE control_parameters,                                                 &
+           ONLY:  message_string
+       IMPLICIT NONE
+       WRITE(message_string,'(A,I8,A)')                                        &
+                         'The maximumn number of agents during this run was',  &
+                         maximum_number_of_agents,                             &
+                         '&Consider adjusting the INPUT parameter'//           &
+                         '&dim_size_agtnum_manual accordingly for the next run.'
+       CALL message( 'mas_data_output_agents', 'PA0457', 0, 0, 0, 6, 0 )
+    END SUBROUTINE mas_last_actions
+!------------------------------------------------------------------------------!
+!--------------------------------------------------------------------------------------------------!
+ SUBROUTINE mas_last_actions
+    USE control_parameters,                                                                        &
+        ONLY:  message_string
+    IMPLICIT NONE
+    WRITE(message_string,'(A,I8,A)') 'The maximumn number of agents during this run was',          &
+                                     maximum_number_of_agents,                                     &
+                                     '&Consider adjusting the INPUT parameter'//                   &
+                                     '&dim_size_agtnum_manual accordingly for the next run.'
+    CALL message( 'mas_data_output_agents', 'PA0457', 0, 0, 0, 6, 0 )
+ END SUBROUTINE mas_last_actions
+!--------------------------------------------------------------------------------------------------!
 ! Description:
 ! ------------
+!> Finds the shortest path from a start position to a target position using the
+!> A*-algorithm
+!------------------------------------------------------------------------------!
+    SUBROUTINE mas_nav_a_star( start_x, start_y, target_x, target_y, nsteps )
+       IMPLICIT NONE
+       LOGICAL ::  target_reached !< flag
+       INTEGER(iwp) ::  cur_node     !< current node of binary heap
+       INTEGER(iwp) ::  il           !< counter (x)
+       INTEGER(iwp) ::  neigh_node   !< neighbor node
+       INTEGER(iwp) ::  node_counter !< binary heap node counter
+       INTEGER(iwp) ::  path_ag      !< index of agent path
+       INTEGER(iwp) ::  som          !< size of mesh
+       INTEGER(iwp) ::  steps        !< steps along the path
+       INTEGER(iwp) ::  nsteps        !< number of steps
+       REAL(wp) ::  start_x      !< x-coordinate agent
+       REAL(wp) ::  start_y      !< y-coordinate agent
+       REAL(wp) ::  new_cost     !< updated cost to reach node
+       REAL(wp) ::  new_priority !< priority of node to be added to queue
+       REAL(wp) ::  rn_gate      !< random number for corner gate
+       REAL(wp) ::  target_x     !< x-coordinate target
+       REAL(wp) ::  target_y     !< y-coordinate target
+!
+!--    Coordinate Type
+       TYPE coord
+          REAL(wp) ::  x   !< x-coordinate
+          REAL(wp) ::  x_s !< x-coordinate (shifted)
+          REAL(wp) ::  y   !< y-coordinate
+          REAL(wp) ::  y_s !< y-coordinate (shifted)
+       END TYPE coord
+       TYPE(coord), DIMENSION(:), ALLOCATABLE, TARGET ::  path     !< path array
+       TYPE(coord), DIMENSION(:), ALLOCATABLE, TARGET ::  tmp_path !< temporary path for resizing
+       node_counter = 0
+!
+!--    Create temporary navigation mesh including agent and target positions
+       CALL mas_nav_create_tmp_mesh( start_x, start_y, target_x, target_y, som )
+       tmp_mesh(som)%cost_so_far = 0.0_wp
+!
+!--    Initialize priority queue
+       heap_count = 0_iwp
+       ALLOCATE(queue(0:100))
+       target_reached = .FALSE.
+!
+!--    Add starting point (agent position) to frontier (the frontier consists
+!--    of all the nodes that are to be visited. The node with the smallest
+!--    priority will be visited first. The priority consists of the distance
+!--    from the start node to this node plus a minimal guess (direct distance)
+!--    from this node to the goal). For the starting node, the priority is set
+!--    to 0, as it's the only node thus far
+       CALL mas_heap_insert_item(som,0.0_wp)
+       cur_node = som
+       DO WHILE ( heap_count > 0 )
+!
+!--       Step one: Pick lowest priority item from queue
+          node_counter = node_counter + 1
+          CALL mas_heap_extract_item(cur_node)
+!
+!--       Node 0 is the goal node
+          IF ( cur_node == 0 ) THEN
+             EXIT
+!> Finds the shortest path from a start position to a target position using the A*-algorithm
+!--------------------------------------------------------------------------------------------------!
+ SUBROUTINE mas_nav_a_star( start_x, start_y, target_x, target_y, nsteps )
+    IMPLICIT NONE
+    INTEGER(iwp) ::  cur_node      !< current node of binary heap
+    INTEGER(iwp) ::  il            !< counter (x)
+    INTEGER(iwp) ::  neigh_node    !< neighbor node
+    INTEGER(iwp) ::  node_counter  !< binary heap node counter
+    INTEGER(iwp) ::  nsteps        !< number of steps
+    INTEGER(iwp) ::  path_ag       !< index of agent path
+    INTEGER(iwp) ::  som           !< size of mesh
+    INTEGER(iwp) ::  steps         !< steps along the path
+    LOGICAL ::  target_reached  !< flag
+    REAL(wp) ::  new_cost      !< updated cost to reach node
+    REAL(wp) ::  new_priority  !< priority of node to be added to queue
+    REAL(wp) ::  start_x       !< x-coordinate agent
+    REAL(wp) ::  start_y       !< y-coordinate agent
+    REAL(wp) ::  rn_gate       !< random number for corner gate
+    REAL(wp) ::  target_x      !< x-coordinate target
+    REAL(wp) ::  target_y      !< y-coordinate target
+!
+!-- Coordinate Type
+    TYPE coord
+       REAL(wp) ::  x    !< x-coordinate
+       REAL(wp) ::  x_s  !< x-coordinate (shifted)
+       REAL(wp) ::  y    !< y-coordinate
+       REAL(wp) ::  y_s  !< y-coordinate (shifted)
+    END TYPE coord
+    TYPE(coord), DIMENSION(:), ALLOCATABLE, TARGET ::  path      !< path array
+    TYPE(coord), DIMENSION(:), ALLOCATABLE, TARGET ::  tmp_path  !< temporary path for resizing
+    node_counter = 0
+!
+!-- Create temporary navigation mesh including agent and target positions
+    CALL mas_nav_create_tmp_mesh( start_x, start_y, target_x, target_y, som )
+    tmp_mesh(som)%cost_so_far = 0.0_wp
+!
+!-- Initialize priority queue
+    heap_count = 0_iwp
+    ALLOCATE( queue(0:100) )
+    target_reached = .FALSE.
+!
+!-- Add starting point (agent position) to frontier (the frontier consists of all the nodes that
+!-- are to be visited. The node with the smallest priority will be visited first. The priority
+!-- consists of the distance from the start node to this node plus a minimal guess (direct
+!-- distance) from this node to the goal). For the starting node, the priority is set to 0, as it's
+!-- the only node thus far.
+    CALL mas_heap_insert_item( som, 0.0_wp )
+    cur_node = som
+    DO WHILE ( heap_count > 0 )
+!
+!--    Step one: Pick lowest priority item from queue
+       node_counter = node_counter + 1
+       CALL mas_heap_extract_item(cur_node)
+!
+!--    Node 0 is the goal node
+       IF ( cur_node == 0 )  THEN
+          EXIT
+       ENDIF
+!
+!--    Loop over all of cur_node's neighbors
+       DO  il = 1, tmp_mesh(cur_node)%noc
+          neigh_node = tmp_mesh(cur_node)%connected_vertices(il)
+!
+!--       Check, if the way from the start node to this neigh_node via cur_node is shorter than the
+!--       previously found shortest path to it.
+!--       If so, replace said cost and add neigh_node to the frontier.
+!--       cost_so_far is initialized as 1.d12 so that all found distances should be smaller.
+          new_cost   = tmp_mesh(cur_node)%cost_so_far + tmp_mesh(cur_node)%distance_to_vertex(il)
+          IF ( new_cost < tmp_mesh(neigh_node)%cost_so_far )  THEN
+             tmp_mesh(neigh_node)%cost_so_far = new_cost
+             tmp_mesh(neigh_node)%origin_id   = cur_node
+!
+!--             Priority in the queue is cost_so_far + heuristic to goal
+             new_priority = new_cost                                                               &
+                            + heuristic(tmp_mesh(neigh_node)%x,                                    &
+                              tmp_mesh(neigh_node)%y, tmp_mesh(0)%x,                               &
+                              tmp_mesh(0)%y)
+             CALL mas_heap_insert_item(neigh_node,new_priority)
           ENDIF
+!
-!--       Loop over all of cur_node's neighbors
-          DO il = 1, tmp_mesh(cur_node)%noc
-             neigh_node = tmp_mesh(cur_node)%connected_vertices(il)
+!
-!--          Check, if the way from the start node to this neigh_node via
-!--          cur_node is shorter than the previously found shortest path to it.
-!--          If so, replace said cost and add neigh_node to the frontier.
-!--          cost_so_far is initialized as 1.d12 so that all found distances
-!--          should be smaller.
-             new_cost   = tmp_mesh(cur_node)%cost_so_far                       &
-                         + tmp_mesh(cur_node)%distance_to_vertex(il)
-             IF ( new_cost < tmp_mesh(neigh_node)%cost_so_far ) THEN
-                tmp_mesh(neigh_node)%cost_so_far = new_cost
-                tmp_mesh(neigh_node)%origin_id   = cur_node
+!
-!--             Priority in the queue is cost_so_far + heuristic to goal
-                new_priority = new_cost                                        &
-                              + heuristic(tmp_mesh(neigh_node)%x,              &
-                                tmp_mesh(neigh_node)%y, tmp_mesh(0)%x,         &
-                                tmp_mesh(0)%y)
-                CALL mas_heap_insert_item(neigh_node,new_priority)
-             ENDIF
-          ENDDO
        ENDDO
+!
+!--    Add nodes to a path array. To do this, we must backtrack from the target
+!--    node to its origin to its origin and so on until an node is reached that
+!--    has no origin (%origin_id == -1). This is the starting node.
+       DEALLOCATE(queue)
+       cur_node = 0
+       steps = 0
+       ALLOCATE(path(1:100))
+       DO WHILE ( cur_node /= -1 )
+          steps = steps + 1
+!
+!--       Resize path array if necessary
+          IF ( steps > SIZE(path) ) THEN
+             ALLOCATE(tmp_path(1:steps-1))
+             tmp_path(1:steps-1) = path(1:steps-1)
+             DEALLOCATE(path)
+             ALLOCATE(path(1:2*(steps-1)))
+             path(1:steps-1) = tmp_path(1:steps-1)
+             DEALLOCATE(tmp_path)
+          ENDIF
+          path(steps)%x = tmp_mesh(cur_node)%x
+          path(steps)%y = tmp_mesh(cur_node)%y
+          path(steps)%x_s = tmp_mesh(cur_node)%x_s
+          path(steps)%y_s = tmp_mesh(cur_node)%y_s
+          cur_node = tmp_mesh(cur_node)%origin_id
+       ENDDO
+!
+!--    Add calculated intermittent targets to the path until either the
+!--    target or the maximum number of intermittent targets is reached.
+!--    Ignore starting point (reduce index by one), it is agent position.
+       dummy_path_x = -1
+       dummy_path_y = -1
+       path_ag = 1
+    ENDDO
+!
+!-- Add nodes to a path array. To do this, we must backtrack from the target node to its origin and
+!-- so on until a node is reached that has no origin (%origin_id == -1). This is the starting node.
+    DEALLOCATE( queue )
+    cur_node = 0
+    steps = 0
+    ALLOCATE( path(1:100) )
+    DO WHILE ( cur_node /= -1 )
+       steps = steps + 1
+!
+!--    Resize path array if necessary
+       IF ( steps > SIZE(path) )  THEN
+          ALLOCATE( tmp_path(1:steps-1) )
+          tmp_path(1:steps-1) = path(1:steps-1)
+          DEALLOCATE( path )
+          ALLOCATE( path(1:2*(steps-1)) )
+          path(1:steps-1) = tmp_path(1:steps-1)
+          DEALLOCATE( tmp_path )
+       ENDIF
+       path(steps)%x = tmp_mesh(cur_node)%x
+       path(steps)%y = tmp_mesh(cur_node)%y
+       path(steps)%x_s = tmp_mesh(cur_node)%x_s
+       path(steps)%y_s = tmp_mesh(cur_node)%y_s
+       cur_node = tmp_mesh(cur_node)%origin_id
+    ENDDO
+!
+!-- Add calculated intermittent targets to the path until either the target or the maximum number of
+!-- intermittent targets is reached.
+!-- Ignore starting point (reduce index by one), it is agent position.
+    dummy_path_x = -1
+    dummy_path_y = -1
+    path_ag = 1
+    steps = steps - 1
+    nsteps = 0
+    DO WHILE( steps > 0 .AND. path_ag <= agt_path_size )
+!
+!--    Each target point is randomly chosen along a line target along the bisector of the building
+!--    corner that starts at corner_gate_start and has a width of corner_gate_width. This is to
+!--    avoid clustering when opposing agent groups try to reach the same corner target.
+       rn_gate = random_function(iran_agent) * corner_gate_width + corner_gate_start
+       dummy_path_x(path_ag) = path(steps)%x + rn_gate * (path(steps)%x_s - path(steps)%x)
+       dummy_path_y(path_ag) = path(steps)%y + rn_gate * (path(steps)%y_s - path(steps)%y)
        steps = steps - 1
+       nsteps = 0
+       DO WHILE( steps > 0 .AND. path_ag <= agt_path_size )
+!
+!--       Each target point is randomly chosen along a line target along the
+!--       bisector of the building corner that starts at corner_gate_start
+!--       and has a width of corner_gate_width. This is to avoid clustering
+!--       when opposing agent groups try to reach the same corner target.
+          rn_gate = random_function(iran_agent) * corner_gate_width            &
+                                                + corner_gate_start
+          dummy_path_x(path_ag) = path(steps)%x + rn_gate                      &
+                         * (path(steps)%x_s - path(steps)%x)
+          dummy_path_y(path_ag) = path(steps)%y + rn_gate                      &
+                         * (path(steps)%y_s - path(steps)%y)
+          steps = steps - 1
+          path_ag = path_ag + 1
+          nsteps = nsteps + 1
+       ENDDO
+!
+!--    Set current intermittent target of this agent
+       DEALLOCATE(tmp_mesh, path)
+    END SUBROUTINE mas_nav_a_star
+!------------------------------------------------------------------------------!
+       path_ag = path_ag + 1
+       nsteps = nsteps + 1
+    ENDDO
+!
+!-- Set current intermittent target of this agent
+    DEALLOCATE( tmp_mesh, path )
+ END SUBROUTINE mas_nav_a_star
+!--------------------------------------------------------------------------------------------------!
 ! Description:
 ! ------------
+!> Adds a connection between two points of the navigation mesh
+!> (one-way: in_mp1 to in_mp2)
+!------------------------------------------------------------------------------!
+    SUBROUTINE mas_nav_add_connection ( in_mp1, id2, in_mp2 )
+       IMPLICIT NONE
+       LOGICAL ::  connection_established  !< Flag to indicate if connection has already been established
+       INTEGER(iwp) ::  id2  !< ID of in_mp2
+       INTEGER(iwp) ::  il   !< local counter
+       INTEGER(iwp) ::  noc1 !< number of connections in in_mp1
+       INTEGER, DIMENSION(:), ALLOCATABLE ::  dum_cv !< dummy array for connected_vertices
+       REAL(wp) ::  dist  !< Distance between the two points
+       REAL(wp), DIMENSION(:), ALLOCATABLE ::  dum_dtv
+       TYPE(mesh_point) ::  in_mp1  !< mesh point that gets a new connection
+       TYPE(mesh_point) ::  in_mp2  !< mesh point in_mp1 will be connected to
+       connection_established = .FALSE.
+!
+!--    Check if connection has already been established
+       noc1 = SIZE(in_mp1%connected_vertices)
+       DO il = 1, in_mp1%noc
+          IF ( in_mp1%connected_vertices(il) == id2 ) THEN
+             connection_established = .TRUE.
+             EXIT
+          ENDIF
+       ENDDO
+       IF ( .NOT. connection_established ) THEN
+!
+!--       Resize arrays, if necessary
+          IF ( in_mp1%noc >= noc1 ) THEN
+             ALLOCATE( dum_cv(1:noc1),dum_dtv(1:noc1) )
+             dum_cv  = in_mp1%connected_vertices
+             dum_dtv = in_mp1%distance_to_vertex
+             DEALLOCATE( in_mp1%connected_vertices, in_mp1%distance_to_vertex )
+             ALLOCATE( in_mp1%connected_vertices(1:2*noc1),                    &
+                       in_mp1%distance_to_vertex(1:2*noc1) )
+             in_mp1%connected_vertices         = -999
+             in_mp1%distance_to_vertex         = -999.
+             in_mp1%connected_vertices(1:noc1) = dum_cv
+             in_mp1%distance_to_vertex(1:noc1) = dum_dtv
+          ENDIF
+!
+!--       Add connection
+          in_mp1%noc = in_mp1%noc+1
+          dist = SQRT( (in_mp1%x - in_mp2%x)**2 + (in_mp1%y - in_mp2%y)**2 )
+          in_mp1%connected_vertices(in_mp1%noc) = id2
+          in_mp1%distance_to_vertex(in_mp1%noc) = dist
+!> Adds a connection between two points of the navigation mesh (one-way: in_mp1 to in_mp2)
+!--------------------------------------------------------------------------------------------------!
+ SUBROUTINE mas_nav_add_connection ( in_mp1, id2, in_mp2 )
+    IMPLICIT NONE
+    LOGICAL ::  connection_established  !< Flag to indicate if connection has already been established
+    INTEGER(iwp) ::  id2   !< ID of in_mp2
+    INTEGER(iwp) ::  il    !< local counter
+    INTEGER(iwp) ::  noc1  !< number of connections in in_mp1
+    INTEGER, DIMENSION(:), ALLOCATABLE ::  dum_cv  !< dummy array for connected_vertices
+    REAL(wp) ::  dist  !< Distance between the two points
+    REAL(wp), DIMENSION(:), ALLOCATABLE ::  dum_dtv
+    TYPE(mesh_point) ::  in_mp1  !< mesh point that gets a new connection
+    TYPE(mesh_point) ::  in_mp2  !< mesh point in_mp1 will be connected to
+    connection_established = .FALSE.
+!
+!-- Check if connection has already been established
+    noc1 = SIZE( in_mp1%connected_vertices )
+    DO  il = 1, in_mp1%noc
+       IF ( in_mp1%connected_vertices(il) == id2 )  THEN
+          connection_established = .TRUE.
+          EXIT
        ENDIF
+    END SUBROUTINE mas_nav_add_connection
+!------------------------------------------------------------------------------!
+    ENDDO
+    IF ( .NOT. connection_established )  THEN
+!
+!--    Resize arrays, if necessary
+       IF ( in_mp1%noc >= noc1 )  THEN
+          ALLOCATE( dum_cv(1:noc1),dum_dtv(1:noc1) )
+          dum_cv  = in_mp1%connected_vertices
+          dum_dtv = in_mp1%distance_to_vertex
+          DEALLOCATE( in_mp1%connected_vertices, in_mp1%distance_to_vertex )
+          ALLOCATE( in_mp1%connected_vertices(1:2*noc1),                                           &
+                    in_mp1%distance_to_vertex(1:2*noc1) )
+          in_mp1%connected_vertices         = -999
+          in_mp1%distance_to_vertex         = -999.
+          in_mp1%connected_vertices(1:noc1) = dum_cv
+          in_mp1%distance_to_vertex(1:noc1) = dum_dtv
+       ENDIF
+!
+!--    Add connection
+       in_mp1%noc = in_mp1%noc+1
+       dist = SQRT( (in_mp1%x - in_mp2%x)**2 + (in_mp1%y - in_mp2%y)**2 )
+       in_mp1%connected_vertices(in_mp1%noc) = id2
+       in_mp1%distance_to_vertex(in_mp1%noc) = dist
+    ENDIF
+ END SUBROUTINE mas_nav_add_connection
+!--------------------------------------------------------------------------------------------------!
 ! Description:
 ! ------------
 !> Adds a vertex (curren position of agent or target) to the existing tmp_mesh
 !------------------------------------------------------------------------------!
     SUBROUTINE mas_nav_add_vertex_to_mesh ( in_mp, in_id )
        IMPLICIT NONE
+       LOGICAL ::  intersection_found !< flag
        INTEGER(iwp) ::  jl    !< mesh point counter
        INTEGER(iwp) ::  pl    !< polygon counter
        INTEGER(iwp) ::  vl    !< vertex counter
        INTEGER(iwp) ::  pid_t !< polygon id of tested mesh point
        INTEGER(iwp) ::  vid_t !< vertex id of tested mesh point
+       INTEGER(iwp) ::  in_id !< vertex id of tested mesh point
        LOGICAL ::  is_left_n  !< local switch
        LOGICAL ::  is_left_p  !< local switch
        LOGICAL ::  is_right_n !< local switch
        LOGICAL ::  is_right_p !< local switch
        REAL(wp) ::  v1x !< x-coordinate of test vertex 1 for intersection test
        REAL(wp) ::  v1y !< y-coordinate of test vertex 1 for intersection test
        REAL(wp) ::  v2x !< x-coordinate of test vertex 2 for intersection test
        REAL(wp) ::  v2y !< y-coordinate of test vertex 2 for intersection test
        REAL(wp) ::  x   !< x-coordinate of current mesh point
        REAL(wp) ::  x_t !< x-coordinate of tested mesh point
        REAL(wp) ::  y   !< y-coordinate of current mesh point
        REAL(wp) ::  y_t !< y-coordinate of tested mesh point
        TYPE(mesh_point) ::  in_mp !< Input mesh point
+!--------------------------------------------------------------------------------------------------!
+ SUBROUTINE mas_nav_add_vertex_to_mesh ( in_mp, in_id )
+    IMPLICIT NONE
+    INTEGER(iwp) ::  in_id  !< vertex id of tested mesh point
+    INTEGER(iwp) ::  jl     !< mesh point counter
+    INTEGER(iwp) ::  pl     !< polygon counter
+    INTEGER(iwp) ::  vl     !< vertex counter
+    INTEGER(iwp) ::  pid_t  !< polygon id of tested mesh point
+    INTEGER(iwp) ::  vid_t  !< vertex id of tested mesh point
+    LOGICAL ::  intersection_found  !< flag
+    LOGICAL ::  is_left_n           !< local switch
+    LOGICAL ::  is_left_p           !< local switch
+    LOGICAL ::  is_right_n          !< local switch
+    LOGICAL ::  is_right_p          !< local switch
+    REAL(wp) ::  v1x  !< x-coordinate of test vertex 1 for intersection test
+    REAL(wp) ::  v1y  !< y-coordinate of test vertex 1 for intersection test
+    REAL(wp) ::  v2x  !< x-coordinate of test vertex 2 for intersection test
+    REAL(wp) ::  v2y  !< y-coordinate of test vertex 2 for intersection test
+    REAL(wp) ::  x    !< x-coordinate of current mesh point
+    REAL(wp) ::  x_t  !< x-coordinate of tested mesh point
+    REAL(wp) ::  y    !< y-coordinate of current mesh point
+    REAL(wp) ::  y_t  !< y-coordinate of tested mesh point
+    TYPE(mesh_point) ::  in_mp  !< Input mesh point
+!
 !--
+       x = in_mp%x
+       y = in_mp%y
+       DO jl = 0, SIZE(tmp_mesh)-2
+          IF ( in_id == jl ) CYCLE
+!
+!--       Ignore mesh points with 0 connections
+          IF ( tmp_mesh(jl)%polygon_id /= -1 ) THEN
+             IF ( tmp_mesh(jl)%noc == 0 ) CYCLE
+          ENDIF
+          x_t = tmp_mesh(jl)%x
+          y_t = tmp_mesh(jl)%y
+          pid_t = tmp_mesh(jl)%polygon_id
+          vid_t = tmp_mesh(jl)%vertex_id
+!
+!--       If the connecting line between the target and a mesh point points
+!--       into the mesh point's polygon, no connection will be
+!--       established between the two points. This is the case if the
+!--       previous (next, n) vertex of the polygon is right of the connecting
+!--       line and the next (previous, p) vertex of the polygon is left of the
+!--       connecting line.
+          IF ( pid_t > 0  .AND.  pid_t <= SIZE( polygons ) )  THEN
+             is_left_p  = is_left(  x, y, x_t, y_t, polygons(pid_t)%vertices(vid_t-1)%x,           &
+                                    polygons(pid_t)%vertices(vid_t-1)%y )
+             is_left_n  = is_left(  x, y, x_t, y_t, polygons(pid_t)%vertices(vid_t+1)%x,           &
+                                    polygons(pid_t)%vertices(vid_t+1)%y )
+             is_right_p = is_right( x, y, x_t, y_t, polygons(pid_t)%vertices(vid_t-1)%x,           &
+                                    polygons(pid_t)%vertices(vid_t-1)%y )
+             is_right_n = is_right( x, y, x_t, y_t, polygons(pid_t)%vertices(vid_t+1)%x,           &
+                                    polygons(pid_t)%vertices(vid_t+1)%y )
+             IF ( ( is_left_p .AND. is_right_n )  .OR.  ( is_right_p .AND. is_left_n ) )  CYCLE
+          ENDIF
+!
+!--       For each edge of each polygon, check if it intersects with the
+!--       potential connection. If at least one intersection is found,
+!--       no connection can be made
+          intersection_found = .FALSE.
+          DO pl = 1, SIZE(polygons)
+             DO vl = 1, polygons(pl)%nov
+                v1x = polygons(pl)%vertices(vl)%x
+                v1y = polygons(pl)%vertices(vl)%y
+                v2x = polygons(pl)%vertices(vl+1)%x
+                v2y = polygons(pl)%vertices(vl+1)%y
+                intersection_found = intersect(x,y,x_t,y_t,v1x,v1y,v2x,v2y)
+                IF ( intersection_found ) THEN
+                   EXIT
+                ENDIF
+             ENDDO
+             IF ( intersection_found ) EXIT
+    x = in_mp%x
+    y = in_mp%y
+    DO  jl = 0, SIZE( tmp_mesh )-2
+       IF ( in_id == jl )  CYCLE
+!
+!--    Ignore mesh points with 0 connections
+       IF ( tmp_mesh(jl)%polygon_id /= -1 )  THEN
+          IF ( tmp_mesh(jl)%noc == 0 )  CYCLE
+       ENDIF
+       x_t = tmp_mesh(jl)%x
+       y_t = tmp_mesh(jl)%y
+       pid_t = tmp_mesh(jl)%polygon_id
+       vid_t = tmp_mesh(jl)%vertex_id
+!
+!--    If the connecting line between the target and a mesh point points into the mesh point's
+!--    polygon, no connection will be established between the two points. This is the case if the
+!--    previous (next, n) vertex of the polygon is right of the connecting line and the next
+!--    (previous, p) vertex of the polygon is left of the connecting line.
+       IF ( pid_t > 0  .AND.  pid_t <= SIZE( polygons ) )  THEN
+          is_left_p  = is_left(  x, y, x_t, y_t, polygons(pid_t)%vertices(vid_t-1)%x,              &
+                                 polygons(pid_t)%vertices(vid_t-1)%y )
+          is_left_n  = is_left(  x, y, x_t, y_t, polygons(pid_t)%vertices(vid_t+1)%x,              &
+                                 polygons(pid_t)%vertices(vid_t+1)%y )
+          is_right_p = is_right( x, y, x_t, y_t, polygons(pid_t)%vertices(vid_t-1)%x,              &
+                                 polygons(pid_t)%vertices(vid_t-1)%y )
+          is_right_n = is_right( x, y, x_t, y_t, polygons(pid_t)%vertices(vid_t+1)%x,              &
+                                 polygons(pid_t)%vertices(vid_t+1)%y )
+          IF ( ( is_left_p .AND. is_right_n )  .OR.  ( is_right_p .AND. is_left_n ) )  CYCLE
+       ENDIF
+!
+!--    For each edge of each polygon, check if it intersects with the potential connection. If at
+!--    least one intersection is found, no connection can be made.
+       intersection_found = .FALSE.
+       DO  pl = 1, SIZE( polygons )
+          DO  vl = 1, polygons(pl)%nov
+             v1x = polygons(pl)%vertices(vl)%x
+             v1y = polygons(pl)%vertices(vl)%y
+             v2x = polygons(pl)%vertices(vl+1)%x
+             v2y = polygons(pl)%vertices(vl+1)%y
+             intersection_found = intersect(x,y,x_t,y_t,v1x,v1y,v2x,v2y)
+             IF ( intersection_found )  THEN
+                EXIT
+             ENDIF
           ENDDO
+          IF ( intersection_found ) CYCLE
+!
+!--       If neither of the above two test was true, a connection will be
+!--       established between the two mesh points.
+          CALL mas_nav_add_connection(in_mp,jl, tmp_mesh(jl))
+          CALL mas_nav_add_connection(tmp_mesh(jl),in_id, in_mp)
+          IF ( intersection_found )  EXIT
        ENDDO
+       CALL mas_nav_reduce_connections(in_mp)
+    END SUBROUTINE mas_nav_add_vertex_to_mesh
+!------------------------------------------------------------------------------!
+       IF ( intersection_found )  CYCLE
+!
+!--    If neither of the above two tests was true, a connection will be established between the two
+!--    mesh points.
+       CALL mas_nav_add_connection(in_mp,jl, tmp_mesh(jl))
+       CALL mas_nav_add_connection(tmp_mesh(jl),in_id, in_mp)
+    ENDDO
+    CALL mas_nav_reduce_connections(in_mp)
+ END SUBROUTINE mas_nav_add_vertex_to_mesh
+!--------------------------------------------------------------------------------------------------!
 ! Description:
 ! ------------
 !> Creates a temporary copy of the navigation mesh to be used for pathfinding
 !------------------------------------------------------------------------------!
     SUBROUTINE mas_nav_create_tmp_mesh( a_x, a_y, t_x, t_y, som )
        IMPLICIT NONE
        INTEGER(iwp) ::  som !< size of mesh
        INTEGER(iwp) ::  noc !< number of connetions
        INTEGER(iwp) ::  im  !< local mesh point counter
        REAL(wp) ::  a_x !< x-coordinate agent
        REAL(wp) ::  a_y !< y-coordinate agent
        REAL(wp) ::  t_x !< x-coordinate target
        REAL(wp) ::  t_y !< y-coordinate target
+!
 !--    give tmp_mesh the size of mesh
        som = SIZE(mesh)+1
        ALLOCATE(tmp_mesh(0:som))
+!
 !--    give the allocatable variables in tmp_mesh their respctive sizes
        DO im = 1, som-1
           noc = mesh(im)%noc
           ALLOCATE(tmp_mesh(im)%connected_vertices(1:noc))
           ALLOCATE(tmp_mesh(im)%distance_to_vertex(1:noc))
        ENDDO
+!
 !--    copy mesh to tmp_mesh
        tmp_mesh(1:som-1) = mesh(1:som-1)
+!
 !--    Add target point ...
        CALL mas_nav_init_mesh_point(tmp_mesh(0),-1_iwp,-1_iwp,t_x, t_y)
        CALL mas_nav_add_vertex_to_mesh(tmp_mesh(0),0_iwp)
+!
 !--    ... and start point to temp mesh
        CALL mas_nav_init_mesh_point(tmp_mesh(som),-1_iwp,-1_iwp,a_x, a_y)
        CALL mas_nav_add_vertex_to_mesh(tmp_mesh(som),som)
     END SUBROUTINE mas_nav_create_tmp_mesh
 !------------------------------------------------------------------------------!
+!--------------------------------------------------------------------------------------------------!
+ SUBROUTINE mas_nav_create_tmp_mesh( a_x, a_y, t_x, t_y, som )
+    IMPLICIT NONE
+    INTEGER(iwp) ::  im   !< local mesh point counter
+    INTEGER(iwp) ::  noc  !< number of connetions
+    INTEGER(iwp) ::  som  !< size of mesh
+    REAL(wp) ::  a_x  !< x-coordinate agent
+    REAL(wp) ::  a_y  !< y-coordinate agent
+    REAL(wp) ::  t_x  !< x-coordinate target
+    REAL(wp) ::  t_y  !< y-coordinate target
+!
+!-- Give tmp_mesh the size of mesh
+    som = SIZE( mesh ) + 1
+    ALLOCATE( tmp_mesh(0:som) )
+!
+!-- Give the allocatable variables in tmp_mesh their respctive sizes
+    DO  im = 1, som-1
+       noc = mesh(im)%noc
+       ALLOCATE( tmp_mesh(im)%connected_vertices(1:noc) )
+       ALLOCATE( tmp_mesh(im)%distance_to_vertex(1:noc) )
+    ENDDO
+!
+!-- Copy mesh to tmp_mesh
+    tmp_mesh(1:som-1) = mesh(1:som-1)
+!
+!-- Add target point ...
+    CALL mas_nav_init_mesh_point(tmp_mesh(0),-1_iwp,-1_iwp,t_x, t_y)
+    CALL mas_nav_add_vertex_to_mesh(tmp_mesh(0),0_iwp)
+!
+!-- ... and start point to temp mesh
+    CALL mas_nav_init_mesh_point(tmp_mesh(som),-1_iwp,-1_iwp,a_x, a_y)
+    CALL mas_nav_add_vertex_to_mesh(tmp_mesh(som),som)
+ END SUBROUTINE mas_nav_create_tmp_mesh
+!--------------------------------------------------------------------------------------------------!
 ! Description:
 ! ------------
+!> Finds the shortest path from an agents' position to her target. As the
+!> actual pathfinding algorithm uses the obstacle corners and then shifts them
+!> outward after pathfinding, cases can uccur in which the connection between
+!> these intermittent targets then intersect with obstacles. To remedy this
+!> the pathfinding algorithm is then run on every two subsequent intermittent
+!> targets iteratively and new intermittent targets may be added to the path
+!> this way.
+!------------------------------------------------------------------------------!
+    SUBROUTINE mas_nav_find_path( nl )
+       IMPLICIT NONE
+       INTEGER(iwp) ::  nl            !< local agent counter
+       INTEGER(iwp) ::  il            !< local counter
+       INTEGER(iwp) ::  jl            !< local counter
+       INTEGER(iwp) ::  kl            !< local counter
+       INTEGER(iwp) ::  nsteps_total  !< number of steps on path
+       INTEGER(iwp) ::  nsteps_dummy  !< number of steps on path
+       REAL(wp), DIMENSION(0:30) ::  ld_path_x !< local dummy agent path to target (x)
+       REAL(wp), DIMENSION(0:30) ::  ld_path_y !< local dummy agent path to target (y)
+!
+!--    Initialize agent path arrays
+       agents(nl)%path_x    = -1
+       agents(nl)%path_y    = -1
+       agents(nl)%path_x(0) = agents(nl)%x
+       agents(nl)%path_y(0) = agents(nl)%y
+!
+!--    Calculate initial path
+       CALL mas_nav_a_star( agents(nl)%x,   agents(nl)%y,                      &
+                            agents(nl)%t_x, agents(nl)%t_y, nsteps_total )
+!
+!--    Set the rest of the agent path that was just calculated
+       agents(nl)%path_x(1:nsteps_total) = dummy_path_x(1:nsteps_total)
+       agents(nl)%path_y(1:nsteps_total) = dummy_path_y(1:nsteps_total)
+!
+!--    Iterate through found path and check more intermittent targets need
+!--    to be added. For this, run pathfinding between every two consecutive
+!--    intermittent targets.
+       DO il = 0, MIN(agt_path_size-1, nsteps_total-1)
+!
+!--       pathfinding between two consecutive intermittent targets
+          CALL mas_nav_a_star( agents(nl)%path_x(il),   agents(nl)%path_y(il), &
+                              agents(nl)%path_x(il+1), agents(nl)%path_y(il+1),&
+                              nsteps_dummy )
+          nsteps_dummy = nsteps_dummy - 1
+!
+!--       If additional intermittent targets are found, add them to the path
+          IF ( nsteps_dummy > 0 ) THEN
+             ld_path_x = -1
+             ld_path_y = -1
+             ld_path_x(il+1:il+nsteps_dummy) = dummy_path_x(1:nsteps_dummy)
+             ld_path_y(il+1:il+nsteps_dummy) = dummy_path_y(1:nsteps_dummy)
+             kl = 1
+             DO jl = il+1,nsteps_total
+               ld_path_x( il+nsteps_dummy+kl ) = agents(nl)%path_x(jl)
+               ld_path_y( il+nsteps_dummy+kl ) = agents(nl)%path_y(jl)
+               kl = kl + 1
+               IF ( kl > agt_path_size ) EXIT
+             ENDDO
+             nsteps_total = MIN(nsteps_total + nsteps_dummy, agt_path_size)
+             agents(nl)%path_x(il+1:nsteps_total) = ld_path_x(il+1:nsteps_total)
+             agents(nl)%path_y(il+1:nsteps_total) = ld_path_y(il+1:nsteps_total)
+          ENDIF
+       ENDDO
+!
+!--    reset path counter to first intermittent target
+       agents(nl)%path_counter = 1
+    END SUBROUTINE mas_nav_find_path
+!------------------------------------------------------------------------------!
+!> Finds the shortest path from an agents' position to her target. As the actual pathfinding
+!> algorithm uses the obstacle corners and then shifts them outward after pathfinding, cases can
+!> occur in which the connection between these intermittent targets then intersect with obstacles.
+!> To remedy this the pathfinding algorithm is then run on every two subsequent intermittent targets
+!> iteratively and new intermittent targets may be added to the path this way.
+!--------------------------------------------------------------------------------------------------!
+ SUBROUTINE mas_nav_find_path( nl )
+    IMPLICIT NONE
+    INTEGER(iwp) ::  il            !< local counter
+    INTEGER(iwp) ::  jl            !< local counter
+    INTEGER(iwp) ::  kl            !< local counter
+    INTEGER(iwp) ::  nl            !< local agent counter
+    INTEGER(iwp) ::  nsteps_dummy  !< number of steps on path
+    INTEGER(iwp) ::  nsteps_total  !< number of steps on path
+    REAL(wp), DIMENSION(0:30) ::  ld_path_x  !< local dummy agent path to target (x)
+    REAL(wp), DIMENSION(0:30) ::  ld_path_y  !< local dummy agent path to target (y)
+!
+!-- Initialize agent path arrays
+    agents(nl)%path_x    = -1
+    agents(nl)%path_y    = -1
+    agents(nl)%path_x(0) = agents(nl)%x
+    agents(nl)%path_y(0) = agents(nl)%y
+!
+!-- Calculate initial path
+    CALL mas_nav_a_star( agents(nl)%x, agents(nl)%y, agents(nl)%t_x, agents(nl)%t_y, nsteps_total )
+!
+!-- Set the rest of the agent path that was just calculated
+    agents(nl)%path_x(1:nsteps_total) = dummy_path_x(1:nsteps_total)
+    agents(nl)%path_y(1:nsteps_total) = dummy_path_y(1:nsteps_total)
+!
+!-- Iterate through found path and check more intermittent targets need to be added. For this, run
+!-- pathfinding between every two consecutive intermittent targets.
+    DO  il = 0, MIN( agt_path_size-1, nsteps_total-1 )
+!
+!--    Pathfinding between two consecutive intermittent targets
+       CALL mas_nav_a_star( agents(nl)%path_x(il),   agents(nl)%path_y(il),                        &
+                            agents(nl)%path_x(il+1), agents(nl)%path_y(il+1),                      &
+                            nsteps_dummy )
+       nsteps_dummy = nsteps_dummy - 1
+!
+!--    If additional intermittent targets are found, add them to the path
+       IF ( nsteps_dummy > 0 )  THEN
+          ld_path_x = -1
+          ld_path_y = -1
+          ld_path_x(il+1:il+nsteps_dummy) = dummy_path_x(1:nsteps_dummy)
+          ld_path_y(il+1:il+nsteps_dummy) = dummy_path_y(1:nsteps_dummy)
+          kl = 1
+          DO  jl = il+1,nsteps_total
+            ld_path_x( il+nsteps_dummy+kl ) = agents(nl)%path_x(jl)
+            ld_path_y( il+nsteps_dummy+kl ) = agents(nl)%path_y(jl)
+            kl = kl + 1
+            IF ( kl > agt_path_size )  EXIT
+          ENDDO
+          nsteps_total = MIN( nsteps_total + nsteps_dummy, agt_path_size )
+          agents(nl)%path_x(il+1:nsteps_total) = ld_path_x(il+1:nsteps_total)
+          agents(nl)%path_y(il+1:nsteps_total) = ld_path_y(il+1:nsteps_total)
+       ENDIF
+    ENDDO
+!
+!-- Reset path counter to first intermittent target
+    agents(nl)%path_counter = 1
+ END SUBROUTINE mas_nav_find_path
+!--------------------------------------------------------------------------------------------------!
 ! Description:
 ! ------------
 !> Reduces the size of connection array to the amount of actual connections
 !> after all connetions were added to a mesh point
 !------------------------------------------------------------------------------!
     SUBROUTINE mas_nav_reduce_connections ( in_mp )
        IMPLICIT NONE
        INTEGER(iwp) ::  noc  !< number of connections
        INTEGER, DIMENSION(:), ALLOCATABLE ::  dum_cv   !< dummy connected_vertices
        REAL(wp), DIMENSION(:), ALLOCATABLE ::  dum_dtv !< dummy distance_to_vertex
        TYPE(mesh_point) ::  in_mp
        noc = in_mp%noc
        ALLOCATE( dum_cv(1:noc),dum_dtv(1:noc) )
        dum_cv  = in_mp%connected_vertices(1:noc)
        dum_dtv = in_mp%distance_to_vertex(1:noc)
        DEALLOCATE( in_mp%connected_vertices, in_mp%distance_to_vertex )
        ALLOCATE( in_mp%connected_vertices(1:noc),                    &
                  in_mp%distance_to_vertex(1:noc) )
        in_mp%connected_vertices(1:noc) = dum_cv(1:noc)
        in_mp%distance_to_vertex(1:noc) = dum_dtv(1:noc)
     END SUBROUTINE mas_nav_reduce_connections
 !------------------------------------------------------------------------------!
+!> Reduces the size of connection array to the amount of actual connections after all connetions
+!> were added to a mesh point
+!--------------------------------------------------------------------------------------------------!
+ SUBROUTINE mas_nav_reduce_connections ( in_mp )
+    IMPLICIT NONE
+    INTEGER(iwp) ::  noc  !< number of connections
+    INTEGER, DIMENSION(:), ALLOCATABLE ::  dum_cv    !< dummy connected_vertices
+    REAL(wp), DIMENSION(:), ALLOCATABLE ::  dum_dtv  !< dummy distance_to_vertex
+    TYPE(mesh_point) ::  in_mp
+    noc = in_mp%noc
+    ALLOCATE( dum_cv(1:noc),dum_dtv(1:noc) )
+    dum_cv  = in_mp%connected_vertices(1:noc)
+    dum_dtv = in_mp%distance_to_vertex(1:noc)
+    DEALLOCATE( in_mp%connected_vertices, in_mp%distance_to_vertex )
+    ALLOCATE( in_mp%connected_vertices(1:noc),                                                     &
+              in_mp%distance_to_vertex(1:noc) )
+    in_mp%connected_vertices(1:noc) = dum_cv(1:noc)
+    in_mp%distance_to_vertex(1:noc) = dum_dtv(1:noc)
+ END SUBROUTINE mas_nav_reduce_connections
+!--------------------------------------------------------------------------------------------------!
 ! Description:
 ! ------------
 !> Initializes a point of the navigation mesh
 !------------------------------------------------------------------------------!
     SUBROUTINE mas_nav_init_mesh_point ( in_mp, pid, vid, x, y )
        IMPLICIT NONE
        INTEGER(iwp) ::  pid !< polygon ID
        INTEGER(iwp) ::  vid !< vertex ID
        REAL(wp) ::  x !< x-coordinate
        REAL(wp) ::  y !< y-coordinate
        TYPE(mesh_point) ::  in_mp !< mesh point to be initialized
        in_mp%origin_id          = -1
        in_mp%polygon_id         = pid
        in_mp%vertex_id          = vid
        in_mp%cost_so_far        = 1.d12
        in_mp%x                  = x
        in_mp%y                  = y
        in_mp%x_s                = x
        in_mp%y_s                = y
        ALLOCATE(in_mp%connected_vertices(1:100),                               &
                 in_mp%distance_to_vertex(1:100))
        in_mp%connected_vertices = -999
        in_mp%distance_to_vertex = -999.
        in_mp%noc                = 0
     END SUBROUTINE mas_nav_init_mesh_point
 !------------------------------------------------------------------------------!
+!--------------------------------------------------------------------------------------------------!
+ SUBROUTINE mas_nav_init_mesh_point ( in_mp, pid, vid, x, y )
+    IMPLICIT NONE
+    INTEGER(iwp) ::  pid  !< polygon ID
+    INTEGER(iwp) ::  vid  !< vertex ID
+    REAL(wp) ::  x  !< x-coordinate
+    REAL(wp) ::  y  !< y-coordinate
+    TYPE(mesh_point) ::  in_mp  !< mesh point to be initialized
+    in_mp%origin_id          = -1
+    in_mp%polygon_id         = pid
+    in_mp%vertex_id          = vid
+    in_mp%cost_so_far        = 1.d12
+    in_mp%x                  = x
+    in_mp%y                  = y
+    in_mp%x_s                = x
+    in_mp%y_s                = y
+    ALLOCATE( in_mp%connected_vertices(1:100),                                                     &
+              in_mp%distance_to_vertex(1:100) )
+    in_mp%connected_vertices = -999
+    in_mp%distance_to_vertex = -999.
+    in_mp%noc                = 0
+ END SUBROUTINE mas_nav_init_mesh_point
+!--------------------------------------------------------------------------------------------------!
 ! Description:
 ! ------------
 !> Reading of namlist from parin file
+!------------------------------------------------------------------------------!
+    SUBROUTINE mas_parin
+       USE control_parameters,                                                 &
+           ONLY: agent_time_unlimited, multi_agent_system_end,                 &
+                 multi_agent_system_start
+       IMPLICIT NONE
+       CHARACTER (LEN=80) ::  line  !<
+       NAMELIST /agent_parameters/  a_rand_target,                             &
+                                    adx,                                       &
+                                    ady,                                       &
+                                    agent_maximum_age,                         &
+                                    agent_time_unlimited,                      &
+                                    alloc_factor_mas,                          &
+                                    asl,                                       &
+                                    asn,                                       &
+                                    asr,                                       &
+                                    ass,                                       &
+                                    at_x,                                      &
+                                    at_y,                                      &
+                                    bc_mas_lr,                                 &
+                                    bc_mas_ns,                                 &
+                                    coll_t_0,                                  &
+                                    corner_gate_start,                         &
+                                    corner_gate_width,                         &
+                                    dim_size_agtnum_manual,                    &
+                                    dim_size_factor_agtnum,                    &
+                                    deallocate_memory_mas,                     &
+                                    dist_to_int_target,                        &
+                                    dt_agent,                                  &
+                                    dt_arel,                                   &
+                                    dt_write_agent_data,                       &
+                                    end_time_arel,                             &
+                                    max_dist_from_path,                        &
+                                    min_nr_agent,                              &
+                                    multi_agent_system_end,                    &
+                                    multi_agent_system_start,                  &
+                                    number_of_agent_groups,                    &
+                                    radius_agent,                              &
+                                    random_start_position_agents,              &
+                                    read_agents_from_restartfile,              &
+                                    repuls_agent,                              &
+                                    repuls_wall,                               &
+                                    scan_radius_agent,                         &
+                                    sigma_rep_agent,                           &
+                                    sigma_rep_wall,                            &
+                                    step_dealloc_mas,                          &
+                                    tau_accel_agent
+!
+!--    Try to find agent package
+       REWIND ( 11 )
+       line = ' '
+       DO WHILE ( INDEX( line, '&agent_parameters' ) == 0 )
+          READ ( 11, '(A)', END=20 )  line
+       ENDDO
+       BACKSPACE ( 11 )
+!
+!--    Read user-defined namelist
+       READ ( 11, agent_parameters, ERR = 10, END = 20 )
+!
+!--    Set flag that indicates that agents are switched on
+       agents_active = .TRUE.
+       GOTO 20
+    BACKSPACE( 11 )
+       READ( 11 , '(A)') line
+       CALL parin_fail_message( 'agent_parameters', line )
+    CONTINUE
+    END SUBROUTINE mas_parin
+!------------------------------------------------------------------------------!
+!--------------------------------------------------------------------------------------------------!
+ SUBROUTINE mas_parin
+    USE control_parameters,                                                                        &
+        ONLY: agent_time_unlimited, multi_agent_system_end, multi_agent_system_start
+    IMPLICIT NONE
+    CHARACTER (LEN=80) ::  line  !<
+    NAMELIST /agent_parameters/  a_rand_target,                                                    &
+                                 adx,                                                              &
+                                 ady,                                                              &
+                                 agent_maximum_age,                                                &
+                                 agent_time_unlimited,                                             &
+                                 alloc_factor_mas,                                                 &
+                                 asl,                                                              &
+                                 asn,                                                              &
+                                 asr,                                                              &
+                                 ass,                                                              &
+                                 at_x,                                                             &
+                                 at_y,                                                             &
+                                 bc_mas_lr,                                                        &
+                                 bc_mas_ns,                                                        &
+                                 coll_t_0,                                                         &
+                                 corner_gate_start,                                                &
+                                 corner_gate_width,                                                &
+                                 deallocate_memory_mas,                                            &
+                                 dim_size_agtnum_manual,                                           &
+                                 dim_size_factor_agtnum,                                           &
+                                 dist_to_int_target,                                               &
+                                 dt_agent,                                                         &
+                                 dt_arel,                                                          &
+                                 dt_write_agent_data,                                              &
+                                 end_time_arel,                                                    &
+                                 max_dist_from_path,                                               &
+                                 min_nr_agent,                                                     &
+                                 multi_agent_system_end,                                           &
+                                 multi_agent_system_start,                                         &
+                                 number_of_agent_groups,                                           &
+                                 radius_agent,                                                     &
+                                 random_start_position_agents,                                     &
+                                 read_agents_from_restartfile,                                     &
+                                 repuls_agent,                                                     &
+                                 repuls_wall,                                                      &
+                                 scan_radius_agent,                                                &
+                                 sigma_rep_agent,                                                  &
+                                 sigma_rep_wall,                                                   &
+                                 step_dealloc_mas,                                                 &
+                                 tau_accel_agent
+!
+!-- Try to find agent package
+    REWIND ( 11 )
+    line = ' '
+    DO WHILE ( INDEX( line, '&agent_parameters' ) == 0 )
+       READ ( 11, '(A)', END=20 )  line
+    ENDDO
+    BACKSPACE ( 11 )
+!
+!-- Read user-defined namelist
+    READ ( 11, agent_parameters, ERR = 10, END = 20 )
+!
+!-- Set flag that indicates that agents are switched on
+    agents_active = .TRUE.
+    GOTO 20
+    BACKSPACE( 11 )
+    READ( 11 , '(A)') line
+    CALL parin_fail_message( 'agent_parameters', line )
+    CONTINUE
+ END SUBROUTINE mas_parin
+!--------------------------------------------------------------------------------------------------!
 ! Description:
 ! ------------
 !> Routine for the whole processor
 !> Sort all agents into the 4 respective subgrid boxes
+!------------------------------------------------------------------------------!
+    SUBROUTINE mas_ps_sort_in_subboxes
+       IMPLICIT NONE
+       INTEGER(iwp) ::  i           !< grid box (x)
+       INTEGER(iwp) ::  ip          !< counter (x)
+       INTEGER(iwp) ::  is          !< box counter
+       INTEGER(iwp) ::  j           !< grid box (y)
+       INTEGER(iwp) ::  jp          !< counter (y)
+       INTEGER(iwp) ::  m           !< sorting index
+       INTEGER(iwp) ::  n           !< agent index
+       INTEGER(iwp) ::  nn          !< agent counter
+       INTEGER(iwp) ::  sort_index  !< sorting index
+       INTEGER(iwp), DIMENSION(0:3) ::  sort_count  !< number of agents in one subbox
+       TYPE(agent_type), DIMENSION(:,:), ALLOCATABLE ::  sort_agents  !< sorted agent array
+       DO  ip = nxl, nxr
+          DO  jp = nys, nyn
+             number_of_agents = agt_count(jp,ip)
+             IF ( number_of_agents <= 0 )  CYCLE
+             agents => grid_agents(jp,ip)%agents(1:number_of_agents)
+             nn = 0
+             sort_count = 0
+             ALLOCATE( sort_agents(number_of_agents, 0:3) )
+             DO  n = 1, number_of_agents
+                sort_index = 0
+                IF ( agents(n)%agent_mask )  THEN
+                   nn = nn + 1
+!
+!--                Sorting agents with a binary scheme
+!--                sort_index=11_2=3_10 -> agent at the left,south subgridbox
+!--                sort_index=10_2=2_10 -> agent at the left,north subgridbox
+!--                sort_index=01_2=1_10 -> agent at the right,south subgridbox
+!--                sort_index=00_2=0_10 -> agent at the right,north subgridbox
+!--                For this the center of the gridbox is calculated
+                   i = (agents(n)%x + 0.5_wp * dx) * ddx
+                   j = (agents(n)%y + 0.5_wp * dy) * ddy
+                   IF ( i == ip )  sort_index = sort_index + 2
+                   IF ( j == jp )  sort_index = sort_index + 1
+                   sort_count(sort_index) = sort_count(sort_index) + 1
+                   m = sort_count(sort_index)
+                   sort_agents(m,sort_index) = agents(n)
+                   sort_agents(m,sort_index)%block_nr = sort_index
+                ENDIF
+!--------------------------------------------------------------------------------------------------!
+ SUBROUTINE mas_ps_sort_in_subboxes
+    IMPLICIT NONE
+    INTEGER(iwp) ::  i           !< grid box (x)
+    INTEGER(iwp) ::  ip          !< counter (x)
+    INTEGER(iwp) ::  is          !< box counter
+    INTEGER(iwp) ::  j           !< grid box (y)
+    INTEGER(iwp) ::  jp          !< counter (y)
+    INTEGER(iwp) ::  m           !< sorting index
+    INTEGER(iwp) ::  n           !< agent index
+    INTEGER(iwp) ::  nn          !< agent counter
+    INTEGER(iwp) ::  sort_index  !< sorting index
+    INTEGER(iwp), DIMENSION(0:3) ::  sort_count  !< number of agents in one subbox
+    TYPE(agent_type), DIMENSION(:,:), ALLOCATABLE ::  sort_agents  !< sorted agent array
+    DO  ip = nxl, nxr
+       DO  jp = nys, nyn
+          number_of_agents = agt_count(jp,ip)
+          IF ( number_of_agents <= 0 )  CYCLE
+          agents => grid_agents(jp,ip)%agents(1:number_of_agents)
+          nn = 0
+          sort_count = 0
+          ALLOCATE( sort_agents(number_of_agents, 0:3) )
+          DO  n = 1, number_of_agents
+             sort_index = 0
+             IF ( agents(n)%agent_mask )  THEN
+                nn = nn + 1
+!
+!--             Sorting agents with a binary scheme
+!--             sort_index=11_2=3_10 -> agent at the left,south subgridbox
+!--             sort_index=10_2=2_10 -> agent at the left,north subgridbox
+!--             sort_index=01_2=1_10 -> agent at the right,south subgridbox
+!--             sort_index=00_2=0_10 -> agent at the right,north subgridbox
+!--             For this the center of the gridbox is calculated
+                i = (agents(n)%x + 0.5_wp * dx) * ddx
+                j = (agents(n)%y + 0.5_wp * dy) * ddy
+                IF ( i == ip )  sort_index = sort_index + 2
+                IF ( j == jp )  sort_index = sort_index + 1
+                sort_count(sort_index) = sort_count(sort_index) + 1
+                m = sort_count(sort_index)
+                sort_agents(m,sort_index) = agents(n)
+                sort_agents(m,sort_index)%block_nr = sort_index
+             ENDIF
+          ENDDO
+          nn = 0
+          DO  is = 0,3
+             grid_agents(jp,ip)%start_index(is) = nn + 1
+             DO  n = 1,sort_count(is)
+                nn = nn + 1
+                agents(nn) = sort_agents(n,is)
              ENDDO
+             nn = 0
+             DO is = 0,3
+                grid_agents(jp,ip)%start_index(is) = nn + 1
+                DO n = 1,sort_count(is)
+                   nn = nn + 1
+                   agents(nn) = sort_agents(n,is)
+                ENDDO
+                grid_agents(jp,ip)%end_index(is) = nn
+             ENDDO
+             number_of_agents = nn
+             agt_count(jp,ip) = number_of_agents
+             DEALLOCATE(sort_agents)
+             grid_agents(jp,ip)%end_index(is) = nn
           ENDDO
+          number_of_agents = nn
+          agt_count(jp,ip) = number_of_agents
+          DEALLOCATE( sort_agents )
        ENDDO
+    END SUBROUTINE mas_ps_sort_in_subboxes
+    ENDDO
+ END SUBROUTINE mas_ps_sort_in_subboxes
 #if defined( __parallel )
 !------------------------------------------------------------------------------!
+!--------------------------------------------------------------------------------------------------!
 ! Description:
 ! ------------
 !> Move all agents not marked for deletion to lowest indices (packing)
+!------------------------------------------------------------------------------!
+    SUBROUTINE mas_ps_pack
+       IMPLICIT NONE
+       INTEGER(iwp) ::  n  !< agent counter
+       INTEGER(iwp) ::  nn !< number of agents
+!
+!--    Find out elements marked for deletion and move data from highest index
+!--    values to these free indices
+       nn = number_of_agents
+       DO WHILE ( .NOT. agents(nn)%agent_mask )
+          nn = nn-1
+          IF ( nn == 0 )  EXIT
+!--------------------------------------------------------------------------------------------------!
+ SUBROUTINE mas_ps_pack
+    IMPLICIT NONE
+    INTEGER(iwp) ::  n   !< agent counter
+    INTEGER(iwp) ::  nn  !< number of agents
+!
+!-- Find out elements marked for deletion and move data from highest index values to these free
+!-- indices.
+    nn = number_of_agents
+    DO WHILE ( .NOT. agents(nn)%agent_mask )
+       nn = nn-1
+       IF ( nn == 0 )  EXIT
+    ENDDO
+    IF ( nn > 0 )  THEN
+       DO  n = 1, number_of_agents
+          IF ( .NOT. agents(n)%agent_mask )  THEN
+             agents(n) = agents(nn)
+             nn = nn - 1
+             DO WHILE ( .NOT. agents(nn)%agent_mask )
+                nn = nn-1
+                IF ( n == nn )  EXIT
+             ENDDO
+          ENDIF
+          IF ( n == nn )  EXIT
        ENDDO
+       IF ( nn > 0 )  THEN
+          DO  n = 1, number_of_agents
+             IF ( .NOT. agents(n)%agent_mask )  THEN
+                agents(n) = agents(nn)
+                nn = nn - 1
+                DO WHILE ( .NOT. agents(nn)%agent_mask )
+                   nn = nn-1
+                   IF ( n == nn )  EXIT
+                ENDDO
+             ENDIF
+             IF ( n == nn )  EXIT
+          ENDDO
+       ENDIF
+!
+!--    The number of deleted agents has been determined in routines
+!--    mas_boundary_conds, mas_droplet_collision, and mas_eh_exchange_horiz
+       number_of_agents = nn
+    END SUBROUTINE mas_ps_pack
+    ENDIF
+!
+!-- The number of deleted agents has been determined in routines mas_boundary_conds,
+!-- mas_droplet_collision, and mas_eh_exchange_horiz.
+    number_of_agents = nn
+ END SUBROUTINE mas_ps_pack
 #endif
 !------------------------------------------------------------------------------!
+!--------------------------------------------------------------------------------------------------!
 ! Description:
 ! ------------
+!> Sort agents in each sub-grid box into two groups: agents that already
+!> completed the LES timestep, and agents that need further timestepping to
+!> complete the LES timestep.
+!------------------------------------------------------------------------------!
+!> Sort agents in each sub-grid box into two groups: agents that already completed the LES
+!> timestep, and agents that need further timestepping to complete the LES timestep.
+!--------------------------------------------------------------------------------------------------!
 !    SUBROUTINE mas_ps_sort_timeloop_done
+!
 !       IMPLICIT NONE
+!
 !       INTEGER(iwp) :: end_index     !< agent end index for each sub-box
 !       INTEGER(iwp) :: i             !< index of agent grid box in x-direction
 !       INTEGER(iwp) :: j             !< index of agent grid box in y-direction
 !       INTEGER(iwp) :: n             !< running index for number of agents
 !       INTEGER(iwp) :: nb            !< index of subgrid boux
 !       INTEGER(iwp) :: nf            !< indices for agents in each sub-box that already finalized their substeps
 !       INTEGER(iwp) :: nnf           !< indices for agents in each sub-box that need further treatment
 !       INTEGER(iwp) :: num_finalized !< number of agents in each sub-box that already finalized their substeps
 !       INTEGER(iwp) :: start_index   !< agent start index for each sub-box
+!       INTEGER(iwp) :: end_index      !< agent end index for each sub-box
+!       INTEGER(iwp) :: i              !< index of agent grid box in x-direction
+!       INTEGER(iwp) :: j              !< index of agent grid box in y-direction
+!       INTEGER(iwp) :: n              !< running index for number of agents
+!       INTEGER(iwp) :: nb             !< index of subgrid boux
+!       INTEGER(iwp) :: nf             !< indices for agents in each sub-box that already finalized their substeps
+!       INTEGER(iwp) :: nnf            !< indices for agents in each sub-box that need further treatment
+!       INTEGER(iwp) :: num_finalized  !< number of agents in each sub-box that already finalized their substeps
+!       INTEGER(iwp) :: start_index    !< agent start index for each sub-box
+!
 !       TYPE(agent_type), DIMENSION(:), ALLOCATABLE :: sort_agents  !< temporary agent array
 …
 !                ALLOCATE( sort_agents(start_index:end_index) )
+!
 !--             Determine number of agents already completed the LES
+!--             Determine number of agents already completed the LES
 !--             timestep, and write them into a temporary array
 !                nf = start_index
 …
 !                ENDDO
+!
 !--             Determine number of agents that not completed the LES
+!--             Determine number of agents that not completed the LES
 !--             timestep, and write them into a temporary array
 !                nnf = nf
 …
 !                                        sort_agents(start_index:end_index)
+!
 !--             Determine updated start_index, used to masked already
 !--             completed agents.
+!--             Determine updated start_index, used to masked already
+!--             completed agents.
 !                grid_agents(j,i)%start_index(nb) =                     &
 !                                   grid_agents(j,i)%start_index(nb)    &
 …
 !                DEALLOCATE ( sort_agents )
+!
 !--             Finally, if number of non-completed agents is non zero
 !--             in any of the sub-boxes, set control flag appropriately.
+!--             Finally, if number of non-completed agents is non zero
+!--             in any of the sub-boxes, set control flag appropriately.
 !                IF ( nnf > nf )                                             &
 !                   grid_agents(j,i)%time_loop_done = .FALSE.
 …
 !    END SUBROUTINE mas_ps_sort_timeloop_done
 !------------------------------------------------------------------------------!
+!--------------------------------------------------------------------------------------------------!
 ! Description:
 ! ------------
 !> Calls social forces calculations
 !------------------------------------------------------------------------------!
     SUBROUTINE mas_timestep_forces_call ( ip, jp )
        IMPLICIT NONE
        INTEGER(iwp) ::  ip  !< counter, x-direction
        INTEGER(iwp) ::  jp  !< counter, y-direction
        INTEGER(iwp) ::  n   !< loop variable over all agents in a grid box
+!
 !--    Get direction for all agents in current grid cell
        CALL mas_agent_direction
        DO n = 1, number_of_agents
           force_x = 0.0_wp
           force_y = 0.0_wp
           CALL mas_timestep_social_forces ( 'acceleration', n, ip, jp )
           CALL mas_timestep_social_forces ( 'other_agents', n, ip, jp )
           CALL mas_timestep_social_forces ( 'walls',        n, ip, jp )
+!
 !--       Update forces
           agents(n)%force_x = force_x
           agents(n)%force_y = force_y
        ENDDO
     END SUBROUTINE mas_timestep_forces_call
 !------------------------------------------------------------------------------!
+!--------------------------------------------------------------------------------------------------!
+ SUBROUTINE mas_timestep_forces_call ( ip, jp )
+    IMPLICIT NONE
+    INTEGER(iwp) ::  ip  !< counter, x-direction
+    INTEGER(iwp) ::  jp  !< counter, y-direction
+    INTEGER(iwp) ::  n   !< loop variable over all agents in a grid box
+!
+!-- Get direction for all agents in current grid cell
+    CALL mas_agent_direction
+    DO  n = 1, number_of_agents
+       force_x = 0.0_wp
+       force_y = 0.0_wp
+       CALL mas_timestep_social_forces ( 'acceleration', n, ip, jp )
+       CALL mas_timestep_social_forces ( 'other_agents', n, ip, jp )
+       CALL mas_timestep_social_forces ( 'walls',        n, ip, jp )
+!
+!--    Update forces
+       agents(n)%force_x = force_x
+       agents(n)%force_y = force_y
+    ENDDO
+ END SUBROUTINE mas_timestep_forces_call
+!--------------------------------------------------------------------------------------------------!
 ! Description:
 ! ------------
 !> Euler timestep of agent transport
+!------------------------------------------------------------------------------!
+    SUBROUTINE mas_timestep
+       IMPLICIT NONE
+       INTEGER(iwp) ::  n !< loop variable over all agents in a grid box
+       REAL(wp) ::  abs_v !< absolute value of velocity
+       REAL(wp) ::  abs_f !< absolute value of force
+       DO n = 1, number_of_agents
+!
+!--       Limit absolute force to a maximum to prevent unrealistic acceleration
+          abs_f = SQRT((agents(n)%force_x)**2 + (agents(n)%force_y)**2)
+          IF ( abs_f > 20. ) THEN
+             agents(n)%force_x = agents(n)%force_x * 20. / abs_f
+             agents(n)%force_y = agents(n)%force_y * 20. / abs_f
+          ENDIF
+!
+!--       Update agent speed
+          agents(n)%speed_x = agents(n)%speed_x + agents(n)%force_x * dt_agent
+          agents(n)%speed_y = agents(n)%speed_y + agents(n)%force_y * dt_agent
+!
+!--       Reduction of agent speed to maximum agent speed
+          abs_v = SQRT((agents(n)%speed_x)**2 + (agents(n)%speed_y)**2)
+          IF ( abs_v > v_max_agent ) THEN
+             agents(n)%speed_x = agents(n)%speed_x * v_max_agent / abs_v
+             agents(n)%speed_y = agents(n)%speed_y * v_max_agent / abs_v
+          ENDIF
+!
+!--       Update agent position
+          agents(n)%x = agents(n)%x + agents(n)%speed_x * dt_agent
+          agents(n)%y = agents(n)%y + agents(n)%speed_y * dt_agent
+!
+!--       Update absolute value of agent speed
+          agents(n)%speed_abs = abs_v
+!
+!--       Increment the agent age and the total time that the agent
+!--       has advanced within the agent timestep procedure
+          agents(n)%age_m  = agents(n)%age
+          agents(n)%age    = agents(n)%age    + dt_agent
+          agents(n)%dt_sum = agents(n)%dt_sum + dt_agent
+!
+!--       Check whether there is still an agent that has not yet completed
+!--       the total LES timestep
+          IF ( ( dt_3d - agents(n)%dt_sum ) > 1E-8_wp )  THEN
+             dt_3d_reached_l_mas = .FALSE.
+          ENDIF
+       ENDDO
+    END SUBROUTINE mas_timestep
+!------------------------------------------------------------------------------!
+!--------------------------------------------------------------------------------------------------!
+ SUBROUTINE mas_timestep
+    IMPLICIT NONE
+    INTEGER(iwp) ::  n  !< loop variable over all agents in a grid box
+    REAL(wp) ::  abs_v  !< absolute value of velocity
+    REAL(wp) ::  abs_f  !< absolute value of force
+    DO  n = 1, number_of_agents
+!
+!--    Limit absolute force to a maximum to prevent unrealistic acceleration
+       abs_f = SQRT( ( agents(n)%force_x )**2 + ( agents(n)%force_y )**2 )
+       IF ( abs_f > 20. )  THEN
+          agents(n)%force_x = agents(n)%force_x * 20. / abs_f
+          agents(n)%force_y = agents(n)%force_y * 20. / abs_f
+       ENDIF
+!
+!--    Update agent speed
+       agents(n)%speed_x = agents(n)%speed_x + agents(n)%force_x * dt_agent
+       agents(n)%speed_y = agents(n)%speed_y + agents(n)%force_y * dt_agent
+!
+!--    Reduction of agent speed to maximum agent speed
+       abs_v = SQRT( ( agents(n)%speed_x )**2 + ( agents(n)%speed_y )**2 )
+       IF ( abs_v > v_max_agent )  THEN
+          agents(n)%speed_x = agents(n)%speed_x * v_max_agent / abs_v
+          agents(n)%speed_y = agents(n)%speed_y * v_max_agent / abs_v
+       ENDIF
+!
+!--    Update agent position
+       agents(n)%x = agents(n)%x + agents(n)%speed_x * dt_agent
+       agents(n)%y = agents(n)%y + agents(n)%speed_y * dt_agent
+!
+!--    Update absolute value of agent speed
+       agents(n)%speed_abs = abs_v
+!
+!--    Increment the agent age and the total time that the agent has advanced within the agent
+!--    timestep procedure
+       agents(n)%age_m  = agents(n)%age
+       agents(n)%age    = agents(n)%age    + dt_agent
+       agents(n)%dt_sum = agents(n)%dt_sum + dt_agent
+!
+!--    Check whether there is still an agent that has not yet completed the total LES timestep
+       IF ( ( dt_3d - agents(n)%dt_sum ) > 1E-8_wp )  THEN
+          dt_3d_reached_l_mas = .FALSE.
+       ENDIF
+    ENDDO
+ END SUBROUTINE mas_timestep
+!--------------------------------------------------------------------------------------------------!
 ! Description:
 ! ------------
+!> Calculates the Social Forces (Helbing and Molnar, 1995) that the agent
+!> experiences due to acceleration towards target and repulsion by obstacles
+!------------------------------------------------------------------------------!
+    SUBROUTINE mas_timestep_social_forces ( mode, nl, ip, jp )
+       IMPLICIT NONE
+       CHARACTER (LEN=*) ::  mode  !< identifier for the mode of calculation
+       INTEGER(iwp) ::  ij_dum      !< index of nearest wall
+       INTEGER(iwp) ::  il          !< index variable along x
+       INTEGER(iwp) ::  ip          !< index variable along x
+       INTEGER(iwp) ::  jl          !< index variable along y
+       INTEGER(iwp) ::  jp          !< index variable along y
+       INTEGER(iwp) ::  nl          !< loop variable over all agents in a grid box
+       INTEGER(iwp) ::  no          !< loop variable over all agents in a grid box
+       INTEGER(iwp) ::  noa         !< amount of agents in a grid box
+       INTEGER(iwp) ::  sc_x_end    !< index for scan for topography/other agents
+       INTEGER(iwp) ::  sc_x_start  !< index for scan for topography/other agents
+       INTEGER(iwp) ::  sc_y_end    !< index for scan for topography/other agents
+       INTEGER(iwp) ::  sc_y_start  !< index for scan for topography/other agents
+       LOGICAL ::  corner_found  !< flag that indicates a corner has been found near agent
+       REAL(wp) ::  a_pl             !< factor for collision avoidance
+       REAL(wp) ::  ax_semimaj       !< semiminor axis of repulsive ellipse
+       REAL(wp) ::  b_pl             !< factor for collision avoidance
+       REAL(wp) ::  c_pl             !< factor for collision avoidance
+       REAL(wp) ::  coll_t           !< time at which the next collision would happen
+       REAL(wp) ::  d_coll_t_0       !< inverse of collision cutoff time
+       REAL(wp) ::  d_pl             !< factor for collision avoidance
+       REAL(wp) ::  ddum_f           !< dummy devisor collision avoidance
+       REAL(wp) ::  dist             !< distance to obstacle
+       REAL(wp) ::  dist_sq          !< distance to obstacle squared
+       REAL(wp) ::  pos_rel_x        !< relative position of two agents (x)
+       REAL(wp) ::  pos_rel_y        !< relative position of two agents (y)
+       REAL(wp) ::  r_sq             !< y-position
+       REAL(wp) ::  sra              !< scan radius (agents)
+       REAL(wp) ::  srw              !< local variable for scan radius (walls)
+       REAL(wp) ::  v_rel_x          !< relative velocity (x); collision avoidance
+       REAL(wp) ::  v_rel_y          !< relative velocity (y); collision avoidance
+       REAL(wp) ::  x_a              !< x-position
+       REAL(wp) ::  x_wall           !< x-position of wall
+       REAL(wp) ::  y_a              !< y-position
+       REAL(wp) ::  y_wall           !< y-position of wall
+       REAL(wp), PARAMETER ::  k_pl = 1.5  !< factor for collision avoidance
+       TYPE(agent_type), DIMENSION(:), POINTER ::  l_agts !< agents that repulse current agent
+!
+!--    Initialization
+       x_a = agents(nl)%x
+       y_a = agents(nl)%y
+       SELECT CASE ( TRIM( mode ) )
+!
+!--       Calculation of force due to agent trying to approach desired velocity
+          CASE ( 'acceleration' )
+             force_x = force_x + d_tau_accel_agent                             &
+                          * ( agents(nl)%speed_des*agents(nl)%speed_e_x        &
+                             -agents(nl)%speed_x )
+             force_y = force_y + d_tau_accel_agent                             &
+                          * ( agents(nl)%speed_des*agents(nl)%speed_e_y        &
+                             -agents(nl)%speed_y )
+!
+!--       Calculation of repulsive forces by other agents in a radius around the
+!--       current one
+          CASE ( 'other_agents' )
+             sra = scan_radius_agent
+             d_coll_t_0 = 1./coll_t_0
+!
+!--          Find relevant gridboxes (those that could contain agents within
+!--          scan radius)
+             sc_x_start = FLOOR( (x_a - sra) * ddx )
+             sc_x_end   = FLOOR( (x_a + sra) * ddx )
+             sc_y_start = FLOOR( (y_a - sra) * ddx )
+             sc_y_end   = FLOOR( (y_a + sra) * ddx )
+             IF ( sc_x_start < nxlg ) sc_x_start = nxlg
+             IF ( sc_x_end   > nxrg ) sc_x_end   = nxrg
+             IF ( sc_y_start < nysg ) sc_y_start = nysg
+             IF ( sc_y_end   > nyng ) sc_y_end   = nyng
+             sra = sra**2
+!
+!--          Loop over all previously found relevant gridboxes
+             DO il = sc_x_start, sc_x_end
+                DO jl = sc_y_start, sc_y_end
+                   noa = agt_count(jl,il)
+                   IF ( noa <= 0 )  CYCLE
+                   l_agts => grid_agents(jl,il)%agents(1:noa)
+                   DO no = 1, noa
+!
+!--                   Skip self
+                      IF ( jl == jp .AND. il == ip .AND. no == nl ) CYCLE
+                      pos_rel_x = l_agts(no)%x - x_a
+                      pos_rel_y = l_agts(no)%y - y_a
+                      dist_sq = pos_rel_x**2 + pos_rel_y**2
+                      IF ( dist_sq > sra ) CYCLE
+                      r_sq    = (2*radius_agent)**2
+                      v_rel_x   = agents(nl)%speed_x - l_agts(no)%speed_x
+                      v_rel_y   = agents(nl)%speed_y - l_agts(no)%speed_y
+!
+!--                   Collision is already occuring, default to standard
+!--                   social forces
+                      IF ( dist_sq <= r_sq ) THEN
+                         dist = SQRT(dist_sq) + 1.0d-12
+                         ax_semimaj = .5_wp*SQRT( dist )
+                         force_x = force_x - 0.125_wp * repuls_agent           &
+                                        * d_sigma_rep_agent / ax_semimaj       &
+                                        * EXP( -ax_semimaj*d_sigma_rep_agent ) &
+                                        * (pos_rel_x/dist)
+                         force_y = force_y - 0.125_wp * repuls_agent           &
+                                        * d_sigma_rep_agent / ax_semimaj       &
+                                        * EXP( -ax_semimaj*d_sigma_rep_agent ) &
+                                        * (pos_rel_y/dist)
+!
+!--                   Currently no collision, calculate collision avoidance
+!--                   force according to Karamouzas et al (2014, PRL 113,238701)
+                      ELSE
+!
+!--                     factors
+                         a_pl = v_rel_x**2 +  v_rel_y**2
+                         b_pl = pos_rel_x*v_rel_x + pos_rel_y*v_rel_y
+                         c_pl = dist_sq - r_sq
+                         d_pl = b_pl**2 - a_pl*c_pl
+!
+!--                      If the two agents are moving non-parallel, calculate
+!--                      collision avoidance social force
+                         IF ( d_pl > 0.0_wp .AND.                              &
+                            ( a_pl < -0.00001 .OR. a_pl > 0.00001 ) )          &
+                         THEN
+                            d_pl   = SQRT(d_pl)
+                            coll_t = (b_pl - d_pl)/a_pl
+                            IF ( coll_t > 0.0_wp ) THEN
+!
+!--                            Dummy factor
+                               ddum_f = 1. / ( a_pl * coll_t**2 )              &
+                                           * ( 2. / coll_t + 1.0 * d_coll_t_0 )
+!
+!--                            x-component of social force
+                               force_x = force_x - k_pl *                      &
+                                         EXP( -coll_t * d_coll_t_0 ) *         &
+                                         ( v_rel_x -                           &
+                                           ( b_pl * v_rel_x -                  &
+                                             a_pl * pos_rel_x ) / d_pl ) *     &
+                                         ddum_f
+!
+!--                            y-component of social force
+                               force_y = force_y - k_pl *                      &
+                                         EXP( -coll_t * d_coll_t_0 ) *         &
+                                         ( v_rel_y -                           &
+                                           ( b_pl * v_rel_y -                  &
+                                             a_pl * pos_rel_y ) / d_pl ) *     &
+                                         ddum_f
+                            ENDIF
+                         ENDIF
+                      ENDIF
+                   ENDDO
+                ENDDO
+             ENDDO
+          CASE ( 'walls' )
+             srw = scan_radius_wall
+             corner_found = .FALSE.
+!
+!--          find relevant grid boxes (those that could contain topography
+!--          within radius)
+             sc_x_start = (x_a - srw) * ddx
+             sc_x_end   = (x_a + srw) * ddx
+             sc_y_start = (y_a - srw) * ddx
+             sc_y_end   = (y_a + srw) * ddx
+             IF ( sc_x_start < nxlg ) sc_x_start = nxlg
+             IF ( sc_x_end   > nxrg ) sc_x_end   = nxrg
+             IF ( sc_y_start < nysg ) sc_y_start = nysg
+             IF ( sc_y_end   > nyng ) sc_y_end   = nyng
+!
+!--          Find "walls" ( i.e. topography steps (up or down) higher than one
+!--          grid box ) that are perpendicular to the agent within the defined
+!--          search radius. Such obstacles cannot be passed and a social force
+!--          to that effect is applied.
+!--          Walls only apply a force perpendicular to the wall to the agent.
+!--          There is therefore a search for walls directly right, left, south
+!--          and north of the agent. All other walls are ignored.
+!--
+!--          Check for wall left of current agent
+             ij_dum = 0
+             IF ( sc_x_start < ip ) THEN
+                DO il = ip - 1, sc_x_start, -1
+!
+!--                Going left from the agent, check for a right wall
+                   IF ( BTEST( obstacle_flags(jp,il), 2 ) ) THEN
+!
+!--                   obstacle found in grid box il, wall at right side
+                      x_wall = (il+1)*dx
+!
+!--                   Calculate force of found wall on agent
+                      CALL mas_timestep_wall_corner_force( x_a, x_wall, y_a,   &
+                                                           y_a )
+!
+!--                   calculate new x starting index for later scan for corners
+                      ij_dum = il + 1
+                      EXIT
+                   ENDIF
+                ENDDO
+             ENDIF
+             IF ( ij_dum /= 0 ) sc_x_start = ij_dum
+!
+!--          Check for wall right of current agent
+             ij_dum = 0
+             IF ( sc_x_end > ip ) THEN
+                DO il = ip + 1, sc_x_end
+!
+!--                Going right from the agent, check for a left wall
+                   IF ( BTEST( obstacle_flags(jp,il), 6 ) ) THEN
+!
+!--                   obstacle found in grid box il, wall at left side
+                      x_wall = il*dx
+!
+!--                   Calculate force of found wall on agent
+                      CALL mas_timestep_wall_corner_force( x_a, x_wall, y_a,   &
+                                                           y_a )
+!
+!--                   calculate new x end index for later scan for corners
+                      ij_dum = il - 1
+                      EXIT
+                   ENDIF
+                ENDDO
+             ENDIF
+             IF ( ij_dum /= 0 ) sc_x_end = ij_dum
+!
+!--          Check for wall south of current agent
+             ij_dum = 0
+             IF ( sc_y_start < jp ) THEN
+                DO jl = jp - 1, sc_y_start, -1
+!
+!--                Going south from the agent, check for a north wall
+                   IF ( BTEST( obstacle_flags(jl,ip), 0 ) ) THEN
+!
+!--                   obstacle found in grid box jl, wall at left side
+                      y_wall = (jl+1)*dy
+                      CALL mas_timestep_wall_corner_force( x_a, x_a, y_a,      &
+                                                           y_wall )
+!
+!--                   calculate new y starting index for later scan for corners
+                      ij_dum = jl + 1
+                      EXIT
+                   ENDIF
+                ENDDO
+             ENDIF
+             IF ( ij_dum /= 0 ) sc_y_start = ij_dum
+!
+!--          Check for wall north of current agent
+             ij_dum = 0
+             IF ( sc_y_end > jp ) THEN
+                DO jl = jp + 1, sc_y_end
+!
+!--                Going north from the agent, check for a south wall
+                   IF ( BTEST( obstacle_flags(jl,ip), 4 ) ) THEN
+!
+!--                   obstacle found in grid box jl, wall at left side
+                      y_wall = jl*dy
+                      CALL mas_timestep_wall_corner_force( x_a, x_a, y_a,      &
+                                                           y_wall )
+!
+!--                   calculate new y end index for later scan for corners
+                      ij_dum = jl - 1
+                   ENDIF
+                ENDDO
+             ENDIF
+             IF ( ij_dum /= 0 ) sc_y_end = ij_dum
+!
+!--          Scan for corners surrounding current agent.
+!--          Only gridcells that are closer than the closest wall in each
+!--          direction (n,s,r,l) are considered in the search since those
+!--          further away would have a significantly smaller resulting force
+!--          than the closer wall.
+             DO il = sc_x_start, sc_x_end
+                DO jl = sc_y_start, sc_y_end
+                   IF ( il == ip .OR. jl == jp ) CYCLE
+!
+!--                corners left of agent
+                   IF ( il < ip ) THEN
+!
+!--                   south left quadrant: look for north right corner
+                      IF ( jl < jp ) THEN
+                         IF ( BTEST( obstacle_flags(jl,il), 1 ) ) THEN
+!
+!--                         calculate coordinates of the found corner
+                            x_wall = (il+1)*dx
+                            y_wall = (jl+1)*dy
+                            CALL mas_timestep_wall_corner_force( x_a, x_wall,  &
+                                                                 y_a, y_wall )
+                         ENDIF
+!
+!--                   north left quadrant: look for south right corner
+                      ELSEIF ( jl > jp ) THEN
+                         IF ( BTEST( obstacle_flags(jl,il), 3 ) ) THEN
+!
+!--                         calculate coordinates of the corner of said gridcell
+!--                         that is closest to the current agent
+                            x_wall = (il+1)*dx
+                            y_wall = jl*dy
+                            CALL mas_timestep_wall_corner_force( x_a, x_wall,  &
+                                                                 y_a, y_wall )
+                         ENDIF
+                      ENDIF
+                   ELSEIF ( il > ip ) THEN
+!
+!--                   south right quadrant: look for north left corner
+                      IF ( jl < jp ) THEN
+                         IF ( BTEST( obstacle_flags(jl,il), 7 ) ) THEN
+!
+!--                         calculate coordinates of the corner of said gridcell
+!--                         that is closest to the current agent
+                            x_wall = il*dx
+                            y_wall = (jl+1)*dy
+                            CALL mas_timestep_wall_corner_force( x_a, x_wall,  &
+                                                                 y_a, y_wall )
+                         ENDIF
+!
+!--                   north right quadrant: look for south left corner
+                      ELSEIF ( jl > jp ) THEN
+                         IF ( BTEST( obstacle_flags(jl,il), 5 ) ) THEN
+!
+!--                         calculate coordinates of the corner of said gridcell
+!--                         that is closest to the current agent
+                            x_wall = il*dx
+                            y_wall = jl*dy
+                            CALL mas_timestep_wall_corner_force( x_a, x_wall,  &
+                                                                 y_a, y_wall )
+!> Calculates the Social Forces (Helbing and Molnar, 1995) that the agent experiences due to
+!> acceleration towards target and repulsion by obstacles
+!--------------------------------------------------------------------------------------------------!
+ SUBROUTINE mas_timestep_social_forces ( mode, nl, ip, jp )
+    IMPLICIT NONE
+    REAL(wp), PARAMETER ::  k_pl = 1.5  !< factor for collision avoidance
+    CHARACTER (LEN=*) ::  mode  !< identifier for the mode of calculation
+    INTEGER(iwp) ::  ij_dum      !< index of nearest wall
+    INTEGER(iwp) ::  il          !< index variable along x
+    INTEGER(iwp) ::  ip          !< index variable along x
+    INTEGER(iwp) ::  jl          !< index variable along y
+    INTEGER(iwp) ::  jp          !< index variable along y
+    INTEGER(iwp) ::  nl          !< loop variable over all agents in a grid box
+    INTEGER(iwp) ::  no          !< loop variable over all agents in a grid box
+    INTEGER(iwp) ::  noa         !< amount of agents in a grid box
+    INTEGER(iwp) ::  sc_x_end    !< index for scan for topography/other agents
+    INTEGER(iwp) ::  sc_x_start  !< index for scan for topography/other agents
+    INTEGER(iwp) ::  sc_y_end    !< index for scan for topography/other agents
+    INTEGER(iwp) ::  sc_y_start  !< index for scan for topography/other agents
+    LOGICAL ::  corner_found  !< flag that indicates a corner has been found near agent
+    REAL(wp) ::  a_pl             !< factor for collision avoidance
+    REAL(wp) ::  ax_semimaj       !< semiminor axis of repulsive ellipse
+    REAL(wp) ::  b_pl             !< factor for collision avoidance
+    REAL(wp) ::  c_pl             !< factor for collision avoidance
+    REAL(wp) ::  coll_t           !< time at which the next collision would happen
+    REAL(wp) ::  d_coll_t_0       !< inverse of collision cutoff time
+    REAL(wp) ::  d_pl             !< factor for collision avoidance
+    REAL(wp) ::  ddum_f           !< dummy devisor collision avoidance
+    REAL(wp) ::  dist             !< distance to obstacle
+    REAL(wp) ::  dist_sq          !< distance to obstacle squared
+    REAL(wp) ::  pos_rel_x        !< relative position of two agents (x)
+    REAL(wp) ::  pos_rel_y        !< relative position of two agents (y)
+    REAL(wp) ::  r_sq             !< y-position
+    REAL(wp) ::  sra              !< scan radius (agents)
+    REAL(wp) ::  srw              !< local variable for scan radius (walls)
+    REAL(wp) ::  v_rel_x          !< relative velocity (x); collision avoidance
+    REAL(wp) ::  v_rel_y          !< relative velocity (y); collision avoidance
+    REAL(wp) ::  x_a              !< x-position
+    REAL(wp) ::  x_wall           !< x-position of wall
+    REAL(wp) ::  y_a              !< y-position
+    REAL(wp) ::  y_wall           !< y-position of wall
+    TYPE(agent_type), DIMENSION(:), POINTER ::  l_agts  !< agents that repulse current agent
+!
+!-- Initialization
+    x_a = agents(nl)%x
+    y_a = agents(nl)%y
+    SELECT CASE ( TRIM( mode ) )
+!
+!--    Calculation of force due to agent trying to approach desired velocity
+       CASE ( 'acceleration' )
+          force_x = force_x + d_tau_accel_agent                                                    &
+                              * ( agents(nl)%speed_des*agents(nl)%speed_e_x - agents(nl)%speed_x )
+          force_y = force_y + d_tau_accel_agent                                                    &
+                              * ( agents(nl)%speed_des*agents(nl)%speed_e_y - agents(nl)%speed_y )
+!
+!--    Calculation of repulsive forces by other agents in a radius around the current one
+       CASE ( 'other_agents' )
+          sra = scan_radius_agent
+          d_coll_t_0 = 1./coll_t_0
+!
+!--       Find relevant gridboxes (those that could contain agents within scan radius)
+          sc_x_start = FLOOR( (x_a - sra) * ddx )
+          sc_x_end   = FLOOR( (x_a + sra) * ddx )
+          sc_y_start = FLOOR( (y_a - sra) * ddx )
+          sc_y_end   = FLOOR( (y_a + sra) * ddx )
+          IF ( sc_x_start < nxlg ) sc_x_start = nxlg
+          IF ( sc_x_end   > nxrg ) sc_x_end   = nxrg
+          IF ( sc_y_start < nysg ) sc_y_start = nysg
+          IF ( sc_y_end   > nyng ) sc_y_end   = nyng
+          sra = sra**2
+!
+!--       Loop over all previously found relevant gridboxes
+          DO  il = sc_x_start, sc_x_end
+             DO  jl = sc_y_start, sc_y_end
+                noa = agt_count(jl,il)
+                IF ( noa <= 0 )  CYCLE
+                l_agts => grid_agents(jl,il)%agents(1:noa)
+                DO  no = 1, noa
+!
+!--                Skip self
+                   IF ( jl == jp  .AND.  il == ip  .AND.  no == nl )  CYCLE
+                   pos_rel_x = l_agts(no)%x - x_a
+                   pos_rel_y = l_agts(no)%y - y_a
+                   dist_sq = pos_rel_x**2 + pos_rel_y**2
+                   IF ( dist_sq > sra )  CYCLE
+                   r_sq    = (2*radius_agent)**2
+                   v_rel_x   = agents(nl)%speed_x - l_agts(no)%speed_x
+                   v_rel_y   = agents(nl)%speed_y - l_agts(no)%speed_y
+!
+!--                Collision is already occuring, default to standard social forces.
+                   IF ( dist_sq <= r_sq )  THEN
+                      dist = SQRT( dist_sq ) + 1.0d-12
+                      ax_semimaj = 0.5_wp * SQRT( dist )
+                      force_x = force_x - 0.125_wp * repuls_agent                                  &
+                                     * d_sigma_rep_agent / ax_semimaj                              &
+                                     * EXP( - ax_semimaj * d_sigma_rep_agent )                     &
+                                     * ( pos_rel_x / dist )
+                      force_y = force_y - 0.125_wp * repuls_agent                                  &
+                                     * d_sigma_rep_agent / ax_semimaj                              &
+                                     * EXP( - ax_semimaj * d_sigma_rep_agent )                     &
+                                     * ( pos_rel_y / dist )
+!
+!--                Currently no collision, calculate collision avoidance force according to
+!--                Karamouzas et al (2014, PRL 113,238701)
+                   ELSE
+!
+!--                   Factors
+                      a_pl = v_rel_x**2 +  v_rel_y**2
+                      b_pl = pos_rel_x*v_rel_x + pos_rel_y*v_rel_y
+                      c_pl = dist_sq - r_sq
+                      d_pl = b_pl**2 - a_pl*c_pl
+!
+!--                   If the two agents are moving non-parallel, calculate collision avoidance
+!--                   social force
+                      IF ( d_pl > 0.0_wp  .AND.  ( a_pl < -0.00001 .OR. a_pl > 0.00001 ) )  THEN
+                         d_pl   = SQRT( d_pl )
+                         coll_t = ( b_pl - d_pl ) / a_pl
+                         IF ( coll_t > 0.0_wp )  THEN
+!
+!--                         Dummy factor
+                            ddum_f = 1. / ( a_pl * coll_t**2 ) * ( 2. / coll_t + 1.0 * d_coll_t_0 )
+!
+!--                         x-component of social force
+                            force_x = force_x - k_pl * EXP( -coll_t * d_coll_t_0 ) *               &
+                                      ( v_rel_x - ( b_pl * v_rel_x - a_pl * pos_rel_x ) / d_pl ) * &
+                                      ddum_f
+!
+!--                         y-component of social force
+                            force_y = force_y - k_pl * EXP( -coll_t * d_coll_t_0 ) *               &
+                                      ( v_rel_y - ( b_pl * v_rel_y - a_pl * pos_rel_y ) / d_pl ) * &
+                                      ddum_f
                          ENDIF
 …
                 ENDDO
              ENDDO
+          CASE DEFAULT
+       END SELECT
+    END SUBROUTINE mas_timestep_social_forces
+!------------------------------------------------------------------------------!
+          ENDDO
+       CASE ( 'walls' )
+          srw = scan_radius_wall
+          corner_found = .FALSE.
+!
+!--       Find relevant grid boxes (those that could contain topography within radius)
+          sc_x_start = (x_a - srw) * ddx
+          sc_x_end   = (x_a + srw) * ddx
+          sc_y_start = (y_a - srw) * ddx
+          sc_y_end   = (y_a + srw) * ddx
+          IF ( sc_x_start < nxlg ) sc_x_start = nxlg
+          IF ( sc_x_end   > nxrg ) sc_x_end   = nxrg
+          IF ( sc_y_start < nysg ) sc_y_start = nysg
+          IF ( sc_y_end   > nyng ) sc_y_end   = nyng
+!
+!--       Find "walls" ( i.e. topography steps (up or down) higher than one grid box ) that are
+!--       perpendicular to the agent within the defined search radius. Such obstacles cannot be
+!--       passed and a social force to that effect is applied.
+!--       Walls only apply a force perpendicular to the wall to the agent.
+!--       There is therefore a search for walls directly right, left, south and north of the agent.
+!--       All other walls are ignored.
+!--
+!--       Check for wall left of current agent
+          ij_dum = 0
+          IF ( sc_x_start < ip )  THEN
+             DO  il = ip - 1, sc_x_start, -1
+!
+!--             Going left from the agent, check for a right wall
+                IF ( BTEST( obstacle_flags(jp,il), 2 ) )  THEN
+!
+!--                Obstacle found in grid box il, wall at right side
+                   x_wall = (il+1)*dx
+!
+!--                Calculate force of found wall on agent
+                   CALL mas_timestep_wall_corner_force( x_a, x_wall, y_a, y_a )
+!
+!--                Calculate new x starting index for later scan for corners
+                   ij_dum = il + 1
+                   EXIT
+                ENDIF
+             ENDDO
+          ENDIF
+          IF ( ij_dum /= 0 ) sc_x_start = ij_dum
+!
+!--       Check for wall right of current agent
+          ij_dum = 0
+          IF ( sc_x_end > ip )  THEN
+             DO  il = ip + 1, sc_x_end
+!
+!--             Going right from the agent, check for a left wall
+                IF ( BTEST( obstacle_flags(jp,il), 6 ) )  THEN
+!
+!--                Obstacle found in grid box il, wall at left side
+                   x_wall = il*dx
+!
+!--                Calculate force of found wall on agent
+                   CALL mas_timestep_wall_corner_force( x_a, x_wall, y_a, y_a )
+!
+!--                Calculate new x end index for later scan for corners
+                   ij_dum = il - 1
+                   EXIT
+                ENDIF
+             ENDDO
+          ENDIF
+          IF ( ij_dum /= 0 ) sc_x_end = ij_dum
+!
+!--          Check for wall south of current agent
+          ij_dum = 0
+          IF ( sc_y_start < jp )  THEN
+             DO  jl = jp - 1, sc_y_start, -1
+!
+!--             Going south from the agent, check for a north wall
+                IF ( BTEST( obstacle_flags(jl,ip), 0 ) )  THEN
+!
+!--                Obstacle found in grid box jl, wall at left side
+                   y_wall = ( jl + 1 ) * dy
+                   CALL mas_timestep_wall_corner_force( x_a, x_a, y_a, y_wall )
+!
+!--                Calculate new y starting index for later scan for corners
+                   ij_dum = jl + 1
+                   EXIT
+                ENDIF
+             ENDDO
+          ENDIF
+          IF ( ij_dum /= 0 ) sc_y_start = ij_dum
+!
+!--       Check for wall north of current agent
+          ij_dum = 0
+          IF ( sc_y_end > jp )  THEN
+             DO  jl = jp + 1, sc_y_end
+!
+!--             Going north from the agent, check for a south wall
+                IF ( BTEST( obstacle_flags(jl,ip), 4 ) )  THEN
+!
+!--                   obstacle found in grid box jl, wall at left side
+                   y_wall = jl * dy
+                   CALL mas_timestep_wall_corner_force( x_a, x_a, y_a, y_wall )
+!
+!--                Calculate new y end index for later scan for corners
+                   ij_dum = jl - 1
+                ENDIF
+             ENDDO
+          ENDIF
+          IF ( ij_dum /= 0 ) sc_y_end = ij_dum
+!
+!--       Scan for corners surrounding current agent.
+!--       Only gridcells that are closer than the closest wall in each direction (n,s,r,l) are
+!--       considered in the search since those further away would have a significantly smaller
+!--       resulting force than the closer wall.
+          DO  il = sc_x_start, sc_x_end
+             DO  jl = sc_y_start, sc_y_end
+                IF ( il == ip  .OR.  jl == jp )  CYCLE
+!
+!--             Corners left of agent
+                IF ( il < ip )  THEN
+!
+!--                South left quadrant: look for north right corner
+                   IF ( jl < jp )  THEN
+                      IF ( BTEST( obstacle_flags(jl,il), 1 ) )  THEN
+!
+!--                      Calculate coordinates of the found corner
+                         x_wall = ( il + 1 ) * dx
+                         y_wall = ( jl + 1 ) * dy
+                         CALL mas_timestep_wall_corner_force( x_a, x_wall, y_a, y_wall )
+                      ENDIF
+!
+!--                North left quadrant: look for south right corner
+                   ELSEIF ( jl > jp )  THEN
+                      IF ( BTEST( obstacle_flags(jl,il), 3 ) )  THEN
+!
+!--                      Calculate coordinates of the corner of mentioned gridcell that is closest
+!--                      to the current agent.
+                         x_wall = ( il + 1 ) * dx
+                         y_wall = jl * dy
+                         CALL mas_timestep_wall_corner_force( x_a, x_wall, y_a, y_wall )
+                      ENDIF
+                   ENDIF
+                ELSEIF ( il > ip )  THEN
+!
+!--                South right quadrant: look for north left corner
+                   IF ( jl < jp )  THEN
+                      IF ( BTEST( obstacle_flags(jl,il), 7 ) )  THEN
+!
+!--                      Calculate coordinates of the corner of mentioned gridcell that is closest
+!--                      to the current agent.
+                         x_wall = il * dx
+                         y_wall = ( jl + 1 ) * dy
+                         CALL mas_timestep_wall_corner_force( x_a, x_wall, y_a, y_wall )
+                      ENDIF
+!
+!--                North right quadrant: look for south left corner
+                   ELSEIF ( jl > jp )  THEN
+                      IF ( BTEST( obstacle_flags(jl,il), 5 ) )  THEN
+!
+!--                      Calculate coordinates of the corner of mentioned gridcell that is closest
+!--                      to the current agent.
+                         x_wall = il * dx
+                         y_wall = jl * dy
+                         CALL mas_timestep_wall_corner_force( x_a, x_wall, y_a, y_wall )
+                      ENDIF
+                   ENDIF
+                ENDIF
+             ENDDO
+          ENDDO
+       CASE DEFAULT
+    END SELECT
+ END SUBROUTINE mas_timestep_social_forces
+!--------------------------------------------------------------------------------------------------!
 ! Description:
 ! ------------
+!> Given a distance to the current agent, calculates the force a found corner
+!> or wall exerts on that agent
+!------------------------------------------------------------------------------!
+    SUBROUTINE mas_timestep_wall_corner_force( xa, xw, ya, yw )
+       IMPLICIT NONE
+       REAL(wp) ::  dist_l     !< distance to obstacle
+       REAL(wp) ::  force_d_x  !< increment of social force, x-direction
+       REAL(wp) ::  force_d_y  !< increment of social force, x-direction
+       REAL(wp) ::  xa         !< x-position of agent
+       REAL(wp) ::  xw         !< x-position of wall
+       REAL(wp) ::  ya         !< x-position of agent
+       REAL(wp) ::  yw         !< y-position of wall
+       force_d_x = 0.0_wp
+       force_d_y = 0.0_wp
+!
+!--    calculate coordinates of corner relative to agent
+!--    postion and distance between corner and agent
+       xw = xa - xw
+       yw = ya - yw
+       dist_l = SQRT( (xw)**2 + (yw)**2 )
+!
+!--    calculate x and y component of repulsive force
+!--    induced by previously found corner
+       IF ( dist_l > 0 ) THEN
+          force_d_x = repuls_wall * d_sigma_rep_wall         &
+                      * EXP( -dist_l * d_sigma_rep_wall )      &
+                      * xw / (dist_l)
+          force_d_y = repuls_wall * d_sigma_rep_wall         &
+                      * EXP( -dist_l * d_sigma_rep_wall )      &
+                      * yw / (dist_l)
+       ENDIF
+! !--    forces that are located outside of a sight radius of
+!> Given a distance to the current agent, calculates the force a found corner or wall exerts on that
+!> agent
+!--------------------------------------------------------------------------------------------------!
+ SUBROUTINE mas_timestep_wall_corner_force( xa, xw, ya, yw )
+    IMPLICIT NONE
+    REAL(wp) ::  dist_l     !< distance to obstacle
+    REAL(wp) ::  force_d_x  !< increment of social force, x-direction
+    REAL(wp) ::  force_d_y  !< increment of social force, x-direction
+    REAL(wp) ::  xa         !< x-position of agent
+    REAL(wp) ::  xw         !< x-position of wall
+    REAL(wp) ::  ya         !< x-position of agent
+    REAL(wp) ::  yw         !< y-position of wall
+    force_d_x = 0.0_wp
+    force_d_y = 0.0_wp
+!
+!-- Calculate coordinates of corner relative to agent postion and distance between corner and agent.
+    xw = xa - xw
+    yw = ya - yw
+    dist_l = SQRT( ( xw )**2 + ( yw )**2 )
+!
+!-- Calculate x and y component of repulsive force induced by previously found corner
+    IF ( dist_l > 0 )  THEN
+       force_d_x = repuls_wall * d_sigma_rep_wall                                                  &
+                   * EXP( -dist_l * d_sigma_rep_wall )                                             &
+                   * xw / (dist_l)
+       force_d_y = repuls_wall * d_sigma_rep_wall                                                  &
+                   * EXP( -dist_l * d_sigma_rep_wall )                                             &
+                   * yw / (dist_l)
+    ENDIF
+! !--    forces that are located outside of a sight radius of
 ! !--    200 degrees (-> COS(100./180.*pi) = COS(.555*pi)) of
 ! !--    current agent are considered to have an effect of 50%
 …
+!
+!--    add force increment to total force of current agent
+       force_x = force_x + force_d_x
+       force_y = force_y + force_d_y
+    END SUBROUTINE mas_timestep_wall_corner_force
+!
+!-- Calculates distance of point P to edge (A,B). If A = B, calculates
+!-- point-to-point distance from A/B to P
+    FUNCTION dist_point_to_edge ( a_x, a_y, b_x, b_y, p_x, p_y )
+       IMPLICIT NONE
+       REAL(wp)  :: ab_x                !< x-coordinate of vector from A to B
+       REAL(wp)  :: ab_y                !< y-coordinate of vector from A to B
+       REAL(wp)  :: ab_d                !< inverse length of vector from A to B
+       REAL(wp)  :: ab_u_x              !< x-coordinate of vector with direction of ab and length 1
+       REAL(wp)  :: ab_u_y              !< y-coordinate of vector with direction of ab and length 1
+       REAL(wp)  :: ba_x                !< x-coordinate of vector from B to A
+       REAL(wp)  :: ba_y                !< y-coordinate of vector from B to A
+       REAL(wp)  :: ap_x                !< x-coordinate of vector from A to P
+       REAL(wp)  :: ap_y                !< y-coordinate of vector from A to P
+       REAL(wp)  :: bp_x                !< x-coordinate of vector from B to P
+       REAL(wp)  :: bp_y                !< y-coordinate of vector from B to P
+       REAL(wp)  :: a_x                 !< x-coordinate of point A of edge
+       REAL(wp)  :: a_y                 !< y-coordinate of point A of edge
+       REAL(wp)  :: b_x                 !< x-coordinate of point B of edge
+       REAL(wp)  :: b_y                 !< y-coordinate of point B of edge
+       REAL(wp)  :: p_x                 !< x-coordinate of point P
+       REAL(wp)  :: p_y                 !< y-coordinate of point P
+       REAL(wp)  :: dist_x              !< x-coordinate of point P
+       REAL(wp)  :: dist_y              !< y-coordinate of point P
+       REAL(wp)  :: dist_point_to_edge  !< y-coordinate of point P
+       ab_x = - a_x + b_x
+       ab_y = - a_y + b_y
+       ba_x = - b_x + a_x
+       ba_y = - b_y + a_y
+       ap_x = - a_x + p_x
+       ap_y = - a_y + p_y
+       bp_x = - b_x + p_x
+       bp_y = - b_y + p_y
+       IF ( ab_x * ap_x + ab_y * ap_y <= 0. ) THEN
+          dist_point_to_edge = SQRT((a_x - p_x)**2 + (a_y - p_y)**2)
+       ELSEIF ( ba_x * bp_x + ba_y * bp_y <= 0. ) THEN
+          dist_point_to_edge = SQRT((b_x - p_x)**2 + (b_y - p_y)**2)
+       ELSE
+          ab_d = 1./SQRT((ab_x)**2+(ab_y)**2)
+          ab_u_x = ab_x*ab_d
+          ab_u_y = ab_y*ab_d
+          dist_x = ap_x - (ap_x*ab_u_x+ap_y*ab_u_y)*ab_u_x
+          dist_y = ap_y - (ap_x*ab_u_x+ap_y*ab_u_y)*ab_u_y
+          dist_point_to_edge = SQRT( dist_x**2 + dist_y**2 )
+!-- Add force increment to total force of current agent
+    force_x = force_x + force_d_x
+    force_y = force_y + force_d_y
+ END SUBROUTINE mas_timestep_wall_corner_force
+!
+!-- Calculates distance of point P to edge (A,B). If A = B, calculates point-to-point distance from
+!-- A/B to P.
+ FUNCTION dist_point_to_edge( a_x, a_y, b_x, b_y, p_x, p_y )
+    IMPLICIT NONE
+    REAL(wp)  :: a_x                 !< x-coordinate of point A of edge
+    REAL(wp)  :: a_y                 !< y-coordinate of point A of edge
+    REAL(wp)  :: ab_x                !< x-coordinate of vector from A to B
+    REAL(wp)  :: ab_y                !< y-coordinate of vector from A to B
+    REAL(wp)  :: ab_d                !< inverse length of vector from A to B
+    REAL(wp)  :: ab_u_x              !< x-coordinate of vector with direction of ab and length 1
+    REAL(wp)  :: ab_u_y              !< y-coordinate of vector with direction of ab and length 1
+    REAL(wp)  :: ap_x                !< x-coordinate of vector from A to P
+    REAL(wp)  :: ap_y                !< y-coordinate of vector from A to P
+    REAL(wp)  :: b_x                 !< x-coordinate of point B of edge
+    REAL(wp)  :: b_y                 !< y-coordinate of point B of edge
+    REAL(wp)  :: ba_x                !< x-coordinate of vector from B to A
+    REAL(wp)  :: ba_y                !< y-coordinate of vector from B to A
+    REAL(wp)  :: bp_x                !< x-coordinate of vector from B to P
+    REAL(wp)  :: bp_y                !< y-coordinate of vector from B to P
+    REAL(wp)  :: dist_x              !< x-coordinate of point P
+    REAL(wp)  :: dist_y              !< y-coordinate of point P
+    REAL(wp)  :: dist_point_to_edge  !< y-coordinate of point P
+    REAL(wp)  :: p_x                 !< x-coordinate of point P
+    REAL(wp)  :: p_y                 !< y-coordinate of point P
+    ab_x = - a_x + b_x
+    ab_y = - a_y + b_y
+    ba_x = - b_x + a_x
+    ba_y = - b_y + a_y
+    ap_x = - a_x + p_x
+    ap_y = - a_y + p_y
+    bp_x = - b_x + p_x
+    bp_y = - b_y + p_y
+    IF ( ab_x * ap_x + ab_y * ap_y <= 0. )  THEN
+       dist_point_to_edge = SQRT( ( a_x - p_x )**2 + ( a_y - p_y )**2 )
+    ELSEIF ( ba_x * bp_x + ba_y * bp_y <= 0. )  THEN
+       dist_point_to_edge = SQRT( ( b_x - p_x )**2 + ( b_y - p_y )**2)
+    ELSE
+       ab_d = 1.0_wp / SQRT( ( ab_x )**2 + ( ab_y )**2 )
+       ab_u_x = ab_x * ab_d
+       ab_u_y = ab_y * ab_d
+       dist_x = ap_x - ( ap_x * ab_u_x + ap_y * ab_u_y ) * ab_u_x
+       dist_y = ap_y - ( ap_x * ab_u_x + ap_y * ab_u_y ) * ab_u_y
+       dist_point_to_edge = SQRT( dist_x**2 + dist_y**2 )
+    ENDIF
+ END FUNCTION dist_point_to_edge
+!
+!-- Returns the heuristic between points A and B (currently the straight distance)
+ FUNCTION heuristic( ax, ay, bx, by )
+    IMPLICIT NONE
+    REAL(wp)  :: ax           !< x-coordinate of point A
+    REAL(wp)  :: ay           !< y-coordinate of point A
+    REAL(wp)  :: bx           !< x-coordinate of point B
+    REAL(wp)  :: by           !< y-coordinate of point B
+    REAL(wp)  :: heuristic    !< return value
+    heuristic = SQRT( ( ax - bx )**2 + ( ay - by )**2 )
+ END FUNCTION heuristic
+!
+!-- Calculates if point P is left of the infinite line that contains A and B (direction: A to B).
+!-- Concept: 2D rotation of two vectors
+ FUNCTION is_left( ax, ay, bx, by, px, py )
+    IMPLICIT NONE
+    LOGICAL  :: is_left !< return value; TRUE if P is left of AB
+    REAL(wp)  :: ax     !< x-coordinate of point A
+    REAL(wp)  :: ay     !< y-coordinate of point A
+    REAL(wp)  :: bx     !< x-coordinate of point B
+    REAL(wp)  :: by     !< y-coordinate of point B
+    REAL(wp)  :: px     !< x-coordinate of point P
+    REAL(wp)  :: py     !< y-coordinate of point P
+    is_left = (bx-ax)*(py-ay)-(px-ax)*(by-ay) > 0
+    IF ( ( ABS( ax - px ) < .001 .AND. ABS( ay - py ) < .001 )  .OR.                               &
+         ( ABS( bx - px ) < .001 .AND. ABS( by - py ) < .001) )                                    &
+    THEN
+       is_left = .FALSE.
+    ENDIF
+ END FUNCTION is_left
+!
+!-- Calculates if point P is right of the infinite line that contains A and B (direction: A to B)
+!-- Concept: 2D rotation of two vectors
+ FUNCTION is_right( ax, ay, bx, by, px, py )
+    IMPLICIT NONE
+    LOGICAL  :: is_right !< return value; TRUE if P is right of AB
+    REAL(wp), INTENT(IN)  :: ax     !< x-coordinate of point A
+    REAL(wp), INTENT(IN)  :: ay     !< y-coordinate of point A
+    REAL(wp), INTENT(IN)  :: bx     !< x-coordinate of point B
+    REAL(wp), INTENT(IN)  :: by     !< y-coordinate of point B
+    REAL(wp), INTENT(IN)  :: px     !< x-coordinate of point P
+    REAL(wp), INTENT(IN)  :: py     !< y-coordinate of point P
+    is_right = (bx-ax)*(py-ay)-(px-ax)*(by-ay) < 0
+    IF ( ( ABS( ax - px ) < 0.001_wp .AND. ABS( ay - py ) < 0.001_wp )  .OR.                       &
+         ( ABS( bx - px ) < 0.001_wp .AND. ABS( by - py ) < 0.001_wp ) )                           &
+    THEN
+       is_right = .FALSE.
+    ENDIF
+ END FUNCTION is_right
+!
+!-- Returns true if the line segments AB and PQ share an intersection
+ FUNCTION intersect( ax, ay, bx, by, px, py, qx, qy )
+    IMPLICIT NONE
+    LOGICAL  :: intersect !< return value; TRUE if intersection was found
+    LOGICAL  :: la        !< T if a is left of PQ
+    LOGICAL  :: lb        !< T if b is left of PQ
+    LOGICAL  :: lp        !< T if p is left of AB
+    LOGICAL  :: lq        !< T if q is left of AB
+    LOGICAL  :: poss      !< flag that indicates if an intersection is still possible
+    LOGICAL  :: ra        !< T if a is right of PQ
+    LOGICAL  :: rb        !< T if b is right of PQ
+    LOGICAL  :: rp        !< T if p is right of AB
+    LOGICAL  :: rq        !< T if q is right of AB
+    REAL(wp)  :: ax     !< x-coordinate of point A
+    REAL(wp)  :: ay     !< y-coordinate of point A
+    REAL(wp)  :: bx     !< x-coordinate of point B
+    REAL(wp)  :: by     !< y-coordinate of point B
+    REAL(wp)  :: px     !< x-coordinate of point P
+    REAL(wp)  :: py     !< y-coordinate of point P
+    REAL(wp)  :: qx     !< x-coordinate of point Q
+    REAL(wp)  :: qy     !< y-coordinate of point Q
+    intersect = .FALSE.
+    poss      = .FALSE.
+!
+!-- Intersection is possible only if P and Q are on opposing sides of AB
+    lp = is_left(ax,ay,bx,by,px,py)
+    rq = is_right(ax,ay,bx,by,qx,qy)
+    IF ( lp  .AND.  rq )  poss = .TRUE.
+    IF ( .NOT. poss )  THEN
+       lq = is_left(ax,ay,bx,by,qx,qy)
+       rp = is_right(ax,ay,bx,by,px,py)
+       IF ( lq  .AND.  rp )  poss = .TRUE.
+    ENDIF
+!
+!-- Intersection occurs only if above test (poss) was true AND A and B are on opposing sides of PQ.
+    IF ( poss )  THEN
+       la = is_left(px,py,qx,qy,ax,ay)
+       rb = is_right(px,py,qx,qy,bx,by)
+       IF ( la  .AND.  rb )  intersect = .TRUE.
+       IF ( .NOT. intersect )  THEN
+          lb = is_left(px,py,qx,qy,bx,by)
+          ra = is_right(px,py,qx,qy,ax,ay)
+          IF ( lb  .AND.  ra )  intersect = .TRUE.
        ENDIF
+    END FUNCTION dist_point_to_edge
+!
+!-- Returns the heuristic between points A and B (currently the straight
+!-- distance)
+    FUNCTION heuristic ( ax, ay, bx, by )
+       IMPLICIT NONE
+       REAL(wp)  :: ax           !< x-coordinate of point A
+       REAL(wp)  :: ay           !< y-coordinate of point A
+       REAL(wp)  :: bx           !< x-coordinate of point B
+       REAL(wp)  :: by           !< y-coordinate of point B
+       REAL(wp)  :: heuristic    !< return value
+       heuristic = SQRT(( ax - bx )**2 + ( ay - by )**2)
+    END FUNCTION heuristic
+!
+!-- Calculates if point P is left of the infinite
+!-- line that contains A and B (direction: A to B)
+!-- Concept: 2D rotation of two vectors
+    FUNCTION is_left ( ax, ay, bx, by, px, py )
+       IMPLICIT NONE
+       LOGICAL  :: is_left !< return value; TRUE if P is left of AB
+       REAL(wp)  :: ax     !< x-coordinate of point A
+       REAL(wp)  :: ay     !< y-coordinate of point A
+       REAL(wp)  :: bx     !< x-coordinate of point B
+       REAL(wp)  :: by     !< y-coordinate of point B
+       REAL(wp)  :: px     !< x-coordinate of point P
+       REAL(wp)  :: py     !< y-coordinate of point P
+       is_left = (bx-ax)*(py-ay)-(px-ax)*(by-ay) > 0
+       IF ( (ABS(ax-px) < .001 .AND. ABS(ay-py) < .001) .OR.                  &
+            (ABS(bx-px) < .001 .AND. ABS(by-py) < .001) )                     &
+       THEN
+          is_left = .FALSE.
+       ENDIF
+       RETURN
+    END FUNCTION is_left
+!
+!-- Calculates if point P is right of the infinite
+!-- line that contains A and B (direction: A to B)
+!-- Concept: 2D rotation of two vectors
+    FUNCTION is_right ( ax, ay, bx, by, px, py )
+       IMPLICIT NONE
+       LOGICAL  :: is_right !< return value; TRUE if P is right of AB
+       REAL(wp), INTENT(IN)  :: ax     !< x-coordinate of point A
+       REAL(wp), INTENT(IN)  :: ay     !< y-coordinate of point A
+       REAL(wp), INTENT(IN)  :: bx     !< x-coordinate of point B
+       REAL(wp), INTENT(IN)  :: by     !< y-coordinate of point B
+       REAL(wp), INTENT(IN)  :: px     !< x-coordinate of point P
+       REAL(wp), INTENT(IN)  :: py     !< y-coordinate of point P
+       is_right = (bx-ax)*(py-ay)-(px-ax)*(by-ay) < 0
+       IF ( (ABS(ax-px) < .001 .AND. ABS(ay-py) < .001) .OR.                  &
+            (ABS(bx-px) < .001 .AND. ABS(by-py) < .001) )                     &
+       THEN
+          is_right = .FALSE.
+       ENDIF
+       RETURN
+    END FUNCTION is_right
+!
+!-- Returns true if the line segments AB and PQ share an intersection
+    FUNCTION intersect ( ax, ay, bx, by, px, py, qx, qy )
+       IMPLICIT NONE
+       LOGICAL  :: intersect !< return value; TRUE if intersection was found
+       LOGICAL  :: la        !< T if a is left of PQ
+       LOGICAL  :: lb        !< T if b is left of PQ
+       LOGICAL  :: lp        !< T if p is left of AB
+       LOGICAL  :: lq        !< T if q is left of AB
+       LOGICAL  :: poss      !< flag that indicates if an intersection is still possible
+       LOGICAL  :: ra        !< T if a is right of PQ
+       LOGICAL  :: rb        !< T if b is right of PQ
+       LOGICAL  :: rp        !< T if p is right of AB
+       LOGICAL  :: rq        !< T if q is right of AB
+       REAL(wp)  :: ax     !< x-coordinate of point A
+       REAL(wp)  :: ay     !< y-coordinate of point A
+       REAL(wp)  :: bx     !< x-coordinate of point B
+       REAL(wp)  :: by     !< y-coordinate of point B
+       REAL(wp)  :: px     !< x-coordinate of point P
+       REAL(wp)  :: py     !< y-coordinate of point P
+       REAL(wp)  :: qx     !< x-coordinate of point Q
+       REAL(wp)  :: qy     !< y-coordinate of point Q
+       intersect = .FALSE.
+       poss      = .FALSE.
+!
+!--    Intersection is possible only if P and Q are on opposing sides of AB
+       lp = is_left(ax,ay,bx,by,px,py)
+       rq = is_right(ax,ay,bx,by,qx,qy)
+       IF ( lp .AND. rq ) poss = .TRUE.
+       IF ( .NOT. poss ) THEN
+          lq = is_left(ax,ay,bx,by,qx,qy)
+          rp = is_right(ax,ay,bx,by,px,py)
+          IF ( lq .AND. rp ) poss = .TRUE.
+       ENDIF
+!
+!--    Intersection occurs only if above test (poss) was true AND
+!--    A and B are on opposing sides of PQ
+       IF ( poss ) THEN
+          la = is_left(px,py,qx,qy,ax,ay)
+          rb = is_right(px,py,qx,qy,bx,by)
+          IF ( la .AND. rb ) intersect = .TRUE.
+          IF ( .NOT. intersect ) THEN
+             lb = is_left(px,py,qx,qy,bx,by)
+             ra = is_right(px,py,qx,qy,ax,ay)
+             IF ( lb .AND. ra ) intersect = .TRUE.
+          ENDIF
+       ENDIF
+       RETURN
+    END FUNCTION intersect
+    ENDIF
+ END FUNCTION intersect
+!
 !-- Gives a nuber randomly distributed around an average
     FUNCTION random_normal ( avg, variation )
        IMPLICIT NONE
        REAL(wp)  :: avg            !< x-coordinate of vector from A to B
        REAL(wp)  :: variation      !< y-coordinate of vector from A to B
        REAL(wp)  :: random_normal  !< y-coordinate of vector from A to B
        REAL(wp), DIMENSION(12)  :: random_arr  !< inverse length of vector from A to B
        CALL RANDOM_NUMBER(random_arr)
        random_normal = avg + variation*(SUM(random_arr)-6.)
     END FUNCTION random_normal
+ FUNCTION random_normal( avg, variation )
+    IMPLICIT NONE
+    REAL(wp)  :: avg            !< x-coordinate of vector from A to B
+    REAL(wp)  :: random_normal  !< y-coordinate of vector from A to B
+    REAL(wp)  :: variation      !< y-coordinate of vector from A to B
+    REAL(wp), DIMENSION(12)  :: random_arr  !< inverse length of vector from A to B
+    CALL RANDOM_NUMBER( random_arr )
+    random_normal = avg + variation * ( SUM( random_arr ) - 6.0_wp )
+ END FUNCTION random_normal

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