SUBROUTINE lpm_pack_arrays

!--------------------------------------------------------------------------------!
! 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 1997-2012  Leibniz University Hannover
!--------------------------------------------------------------------------------!
!
! Current revisions:
! ------------------
! 
!
! Former revisions:
! -----------------
! $Id: lpm_pack_arrays.f90 1037 2012-10-22 14:10:22Z fricke $
!
! 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:
! ------------
! Pack particle and tail arrays, which means eliminate those elements marked for
! deletion and move data with higher index values to these free indices.
! Determine the new number of particles.
!------------------------------------------------------------------------------!

    USE particle_attributes

    IMPLICIT NONE

    INTEGER ::  n, nd, nn


!
!-- Find out elements marked for deletion and move data with higher index
!-- values to these free indices
    nn = 0
    nd = 0

    DO  n = 1, number_of_particles

       IF ( particle_mask(n) )  THEN
          nn = nn + 1
          particles(nn) = particles(n)
       ELSE
          nd = nd + 1
       ENDIF

    ENDDO
!
!-- The number of deleted particles has been determined in routines
!-- lpm_boundary_conds, lpm_droplet_collision, and lpm_exchange_horiz
    number_of_particles = number_of_particles - deleted_particles

!
!-- Handle tail array in the same way, store the new tail ids and re-assign it
!-- to the respective particles
    IF ( use_particle_tails )  THEN

       nn = 0
       nd = 0

       DO  n = 1, number_of_tails

          IF ( tail_mask(n) )  THEN
             nn = nn + 1
             particle_tail_coordinates(:,:,nn) = &
                                                particle_tail_coordinates(:,:,n)
             new_tail_id(n) = nn
          ELSE
             nd = nd + 1
          ENDIF

       ENDDO

       DO  n = 1, number_of_particles
          IF ( particles(n)%tail_id /= 0 )  THEN
             particles(n)%tail_id = new_tail_id(particles(n)%tail_id)
          ENDIF
       ENDDO

    ENDIF

!
!-- The number of deleted tails has been determined in routines
!-- lpm_boundary_conds and lpm_exchange_horiz
    number_of_tails = number_of_tails - deleted_tails


 END SUBROUTINE lpm_pack_arrays