SUBROUTINE lpm_release_set

!------------------------------------------------------------------------------!
! Current revisions:
! ------------------
! 
!
! Former revisions:
! -----------------
! $Id: lpm_release_set.f90 850 2012-03-15 12:09:25Z letzel $
!
! 849 2012-03-15 10:35:09Z raasch
! initial revision (former part of advec_particles)
!
!
! Description:
! ------------
! Release a new set of particles and, if required, particle tails. These
! particles/tails are added at the end of the existing arrays. Extend the
! respective particle and tail arrays, if neccessary.
!------------------------------------------------------------------------------!

    USE control_parameters
    USE grid_variables
    USE indices
    USE particle_attributes
    USE random_function_mod

    IMPLICIT NONE

    INTEGER ::  ie, is, n, nn


!
!-- Check, if particle storage must be extended
    IF ( number_of_particles + number_of_initial_particles > &
         maximum_number_of_particles  )  THEN
       IF ( netcdf_output  .AND.  netcdf_data_format < 3 )  THEN
          message_string = 'maximum_number_of_particles needs to be increa' // &
                           'sed &but this is not allowed with netcdf_data_' // &
                           'format < 3'
          CALL message( 'lpm_release_set', 'PA0146', 2, 2, -1, 6, 1 )
       ELSE
          CALL lpm_extend_particle_array( number_of_initial_particles )
       ENDIF
    ENDIF

!
!-- Check, if tail storage must be extended
    IF ( use_particle_tails )  THEN
       IF ( number_of_tails + number_of_initial_tails > &
            maximum_number_of_tails  )  THEN
          IF ( netcdf_output  .AND.  netcdf_data_format < 3 )  THEN
             message_string = 'maximum_number_of_tails needs to be increas' // &
                              'ed &but this is not allowed with netcdf_dat' // &
                              'a_format < 3'
             CALL message( 'lpm_release_set', 'PA0147', 2, 2, -1, 6, 1 )
          ELSE
             CALL lpm_extend_tail_array( number_of_initial_tails )
          ENDIF
       ENDIF
    ENDIF

    IF ( number_of_initial_particles /= 0 )  THEN

       is = number_of_particles + 1
       ie = number_of_particles + number_of_initial_particles
       particles(is:ie) = initial_particles(1:number_of_initial_particles)
!
!--    Add random fluctuation to particle positions. Particles should
!--    remain in the subdomain.
       IF ( random_start_position )  THEN

          DO  n = is, ie

             IF ( psl(particles(n)%group) /= psr(particles(n)%group) )  THEN
                particles(n)%x = particles(n)%x +                         &
                                 ( random_function( iran_part ) - 0.5 ) * &
                                 pdx(particles(n)%group)
                IF ( particles(n)%x  <=  ( nxl - 0.5 ) * dx )  THEN
                   particles(n)%x = ( nxl - 0.4999999999 ) * dx
                ELSEIF ( particles(n)%x  >=  ( nxr + 0.5 ) * dx )  THEN
                   particles(n)%x = ( nxr + 0.4999999999 ) * dx
                ENDIF
             ENDIF

             IF ( pss(particles(n)%group) /= psn(particles(n)%group) )  THEN
                particles(n)%y = particles(n)%y +                         &
                                 ( random_function( iran_part ) - 0.5 ) * &
                                 pdy(particles(n)%group)
                IF ( particles(n)%y  <=  ( nys - 0.5 ) * dy )  THEN
                   particles(n)%y = ( nys - 0.4999999999 ) * dy
                ELSEIF ( particles(n)%y  >=  ( nyn + 0.5 ) * dy )  THEN
                   particles(n)%y = ( nyn + 0.4999999999 ) * dy
                ENDIF
             ENDIF

             IF ( psb(particles(n)%group) /= pst(particles(n)%group) )  THEN
                particles(n)%z = particles(n)%z +                         &
                                 ( random_function( iran_part ) - 0.5 ) * &
                                 pdz(particles(n)%group)
             ENDIF

          ENDDO

       ENDIF

!
!--    Set the beginning of the new particle tails and their age
       IF ( use_particle_tails )  THEN

          DO  n = is, ie
!
!--          New particles which should have a tail, already have got a
!--          provisional tail id unequal zero (see lpm_init)
             IF ( particles(n)%tail_id /= 0 )  THEN

                number_of_tails = number_of_tails + 1
                nn = number_of_tails
                particles(n)%tail_id = nn   ! set the final tail id
                particle_tail_coordinates(1,1,nn) = particles(n)%x
                particle_tail_coordinates(1,2,nn) = particles(n)%y
                particle_tail_coordinates(1,3,nn) = particles(n)%z
                particle_tail_coordinates(1,4,nn) = particles(n)%class
                particles(n)%tailpoints = 1

                IF ( minimum_tailpoint_distance /= 0.0 )  THEN
                   particle_tail_coordinates(2,1,nn) = particles(n)%x
                   particle_tail_coordinates(2,2,nn) = particles(n)%y
                   particle_tail_coordinates(2,3,nn) = particles(n)%z
                   particle_tail_coordinates(2,4,nn) = particles(n)%class
                   particle_tail_coordinates(1:2,5,nn) = 0.0
                   particles(n)%tailpoints = 2
                ENDIF

             ENDIF

          ENDDO

       ENDIF

       number_of_particles = number_of_particles + number_of_initial_particles

    ENDIF

 END SUBROUTINE lpm_release_set