SUBROUTINE lpm_pack_arrays

!------------------------------------------------------------------------------!
! Current revisions:
! ------------------
! 
!
! Former revisions:
! -----------------
! $Id: lpm_pack_arrays.f90 850 2012-03-15 12:09:25Z hoffmann $
!
! 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