SUBROUTINE lpm_write_restart_file

!--------------------------------------------------------------------------------!
! This file is part of PALM.
!
! 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 1997-2014 Leibniz Universitaet Hannover
!--------------------------------------------------------------------------------!
!
! Current revisions:
! ------------------
! 
! 
! Former revisions:
! -----------------
! $Id: lpm_write_restart_file.f90 1360 2014-04-11 17:20:32Z witha $
!
! 1359 2014-04-11 17:15:14Z hoffmann
! New particle structure integrated. 
!
! 1320 2014-03-20 08:40:49Z raasch
! ONLY-attribute added to USE-statements,
! kind-parameters added to all INTEGER and REAL declaration statements,
! kinds are defined in new module kinds,
! comment fields (!:) to be used for variable explanations added to
! all variable declaration statements
!
! 1036 2012-10-22 13:43:42Z raasch
! code put under GPL (PALM 3.9)
!
! 849 2012-03-15 10:35:09Z raasch
! initial revision (former part of advec_particles)
!
!
! Description:
! ------------
! Write particle data in FORTRAN binary format on restart file
!------------------------------------------------------------------------------!

    USE control_parameters,                                                    &
        ONLY:  io_blocks, io_group

    USE indices,                                                               &
        ONLY:  nxl, nxr, nyn, nys, nzb, nzt

    USE kinds

    USE particle_attributes,                                                   &
        ONLY:  bc_par_b, bc_par_lr, bc_par_ns, bc_par_t, grid_particles,       &
               maximum_number_of_tails, maximum_number_of_tailpoints,          &
               number_of_particles, number_of_particle_groups,                 &
               number_of_tails, particles, particle_groups,                    &
               particle_tail_coordinates, prt_count, time_prel,                &
               time_write_particle_data, uniform_particles,                    &
               use_particle_tails, zero_particle

    USE pegrid

    IMPLICIT NONE

    CHARACTER (LEN=10) ::  particle_binary_version   !:

    INTEGER(iwp) ::  i                               !:
    INTEGER(iwp) ::  ip                              !:
    INTEGER(iwp) ::  jp                              !:
    INTEGER(iwp) ::  kp                              !:

!
!-- First open the output unit.
    IF ( myid_char == '' )  THEN
       OPEN ( 90, FILE='PARTICLE_RESTART_DATA_OUT'//myid_char, &
                  FORM='UNFORMATTED')
    ELSE
       IF ( myid == 0 )  CALL local_system( 'mkdir PARTICLE_RESTART_DATA_OUT' )
#if defined( __parallel )
!
!--    Set a barrier in order to allow that thereafter all other processors
!--    in the directory created by PE0 can open their file
       CALL MPI_BARRIER( comm2d, ierr )
#endif
       OPEN ( 90, FILE='PARTICLE_RESTART_DATA_OUT/'//myid_char, &
                  FORM='UNFORMATTED' )
    ENDIF

!    DO  i = 0, io_blocks-1

!       IF ( i == io_group )  THEN

!
!--       Write the version number of the binary format.
!--       Attention: After changes to the following output commands the version
!--       ---------  number of the variable particle_binary_version must be
!--                  changed! Also, the version number and the list of arrays
!--                  to be read in lpm_read_restart_file must be adjusted
!--                  accordingly.
          particle_binary_version = '3.2'
          WRITE ( 90 )  particle_binary_version

!
!--       Write some particle parameters, the size of the particle arrays as
!--       well as other dvrp-plot variables.
          WRITE ( 90 )  bc_par_b, bc_par_lr, bc_par_ns, bc_par_t,              &
                        maximum_number_of_tailpoints, maximum_number_of_tails, &
                        number_of_particle_groups, number_of_tails,            &
                        particle_groups, time_prel, time_write_particle_data,  &
                        uniform_particles

          WRITE ( 90 )  prt_count
          
          DO  ip = nxl, nxr
             DO  jp = nys, nyn
                DO  kp = nzb+1, nzt
                   number_of_particles = prt_count(kp,jp,ip)
                   particles => grid_particles(kp,jp,ip)%particles(1:number_of_particles)
                   IF ( number_of_particles <= 0 )  CYCLE
                   WRITE ( 90 )  particles
                ENDDO
             ENDDO
          ENDDO

!
!--       particle tails currently not available
!          IF ( use_particle_tails )  THEN
!             WRITE ( 90 )  particle_tail_coordinates
!          ENDIF

          CLOSE ( 90 )

!       ENDIF

#if defined( __parallel )
       CALL MPI_BARRIER( comm2d, ierr )
#endif

 !   ENDDO


 END SUBROUTINE lpm_write_restart_file