SUBROUTINE set_particle_attributes

!------------------------------------------------------------------------------!
! Actual revisions:
! -----------------
! 
!
! Former revisions:
! -----------------
! $Id: set_particle_attributes.f90 264 2009-03-21 08:14:44Z letzel $
!
! Initial version (2009/03/21)
!
! Description:
! ------------
! This routine sets certain particle attributes depending on the values that
! other PALM variables have at the current particle position.
!------------------------------------------------------------------------------!

    USE arrays_3d
    USE control_parameters
    USE cpulog
    USE dvrp_variables
    USE grid_variables
    USE indices
    USE interfaces
    USE particle_attributes
    USE pegrid
    USE statistics

    IMPLICIT NONE

    INTEGER ::  i, j, k, n
    REAL    ::  aa, bb, cc, dd, gg, pt_int, pt_int_l, pt_int_u, w_int, &
                w_int_l, w_int_u, x, y


    CALL cpu_log( log_point_s(49), 'set_particle_attributes', 'start' )

!
!-- Set particle color
    IF ( particle_color == 'absuv' )  THEN

    ELSEIF ( particle_color == 'pt*' )  THEN
!
!--    Set particle color depending on the resolved scale temperature
!--    fluctuation.
!--    First, calculate the horizontal average of the potential temperature
!--    (This is also done in flow_statistics, but flow_statistics is called
!--    after this routine.)
       sums_l(:,4,0) = 0.0
       DO  i = nxl, nxr
          DO  j =  nys, nyn
             DO  k = nzb, nzt+1
                sums_l(k,4,0) = sums_l(k,4,0) + pt(k,j,i)
             ENDDO
          ENDDO
       ENDDO

#if defined( __parallel )

       CALL MPI_ALLREDUCE( sums_l(nzb,4,0), sums(nzb,4), nzt+2-nzb, &
                           MPI_REAL, MPI_SUM, comm2d, ierr )

#else

       sums(:,4) = sums_l(:,4,0)

#endif

       sums(:,4) = sums(:,4) / ngp_2dh(0)

       DO  n = 1, number_of_particles
!
!--       Interpolate temperature to the current particle position
          i = particles(n)%x * ddx
          j = particles(n)%y * ddy
          k = ( particles(n)%z + 0.5 * dz * atmos_ocean_sign ) / dz  &
              + offset_ocean_nzt                     ! only exact if equidistant

          x  = particles(n)%x - i * dx
          y  = particles(n)%y - j * dy
          aa = x**2          + y**2
          bb = ( dx - x )**2 + y**2
          cc = x**2          + ( dy - y )**2
          dd = ( dx - x )**2 + ( dy - y )**2
          gg = aa + bb + cc + dd

          pt_int_l = ( ( gg - aa ) * pt(k,j,i)   + ( gg - bb ) * pt(k,j,i+1)   &
                     + ( gg - cc ) * pt(k,j+1,i) + ( gg - dd ) * pt(k,j+1,i+1) &
                     ) / ( 3.0 * gg ) - sums(k,4)

          pt_int_u = ( ( gg-aa ) * pt(k+1,j,i)   + ( gg-bb ) * pt(k+1,j,i+1)   &
                     + ( gg-cc ) * pt(k+1,j+1,i) + ( gg-dd ) * pt(k+1,j+1,i+1) &
                     ) / ( 3.0 * gg ) - sums(k,4)

          pt_int = pt_int_l + ( particles(n)%z - zu(k) ) / dz * &
                              ( pt_int_u - pt_int_l )

!
!--       Limit values by the given interval and normalize to interval [0,1]
          pt_int = MIN( pt_int, color_interval(2) )
          pt_int = MAX( pt_int, color_interval(1) )

          pt_int = ( pt_int - color_interval(1) ) / &
                   ( color_interval(2) - color_interval(1) )

!
!--       Number of available colors is defined in init_dvrp
          particles(n)%color = 1 + pt_int * ( dvrp_colortable_entries_prt - 1 )

    ENDDO

    ELSEIF ( particle_color == 'z' )  THEN

    ENDIF

!
!-- Set particle size for dvrp graphics
    IF ( particle_dvrpsize == 'absw' )  THEN

       DO  n = 1, number_of_particles
!
!--       Interpolate w-component to the current particle position
          i = particles(n)%x * ddx
          j = particles(n)%y * ddy
          k = particles(n)%z / dz

          x  = particles(n)%x - i * dx
          y  = particles(n)%y - j * dy
          aa = x**2          + y**2
          bb = ( dx - x )**2 + y**2
          cc = x**2          + ( dy - y )**2
          dd = ( dx - x )**2 + ( dy - y )**2
          gg = aa + bb + cc + dd

          w_int_l = ( ( gg - aa ) * w(k,j,i)   + ( gg - bb ) * w(k,j,i+1)   &
                    + ( gg - cc ) * w(k,j+1,i) + ( gg - dd ) * w(k,j+1,i+1) &
                    ) / ( 3.0 * gg )

          IF ( k+1 == nzt+1 )  THEN
             w_int = w_int_l
          ELSE
             w_int_u = ( ( gg-aa ) * w(k+1,j,i)   + ( gg-bb ) * w(k+1,j,i+1)   &
                       + ( gg-cc ) * w(k+1,j+1,i) + ( gg-dd ) * w(k+1,j+1,i+1) &
                       ) / ( 3.0 * gg )
             w_int = w_int_l + ( particles(n)%z - zw(k) ) / dz * &
                               ( w_int_u - w_int_l )
          ENDIF

          particles(n)%dvrp_psize = ( 0.2 + MIN( 0.6, ABS( w_int ) / 6.0 ) ) * &
                                    dx * 1.4

       ENDDO

    ENDIF

    CALL cpu_log( log_point_s(49), 'set_particle_attributes', 'stop' )


 END SUBROUTINE set_particle_attributes