SUBROUTINE user_statistics( mode, sr, tn )

!--------------------------------------------------------------------------------!
! 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: user_statistics.f90 1321 2014-03-20 09:40:40Z maronga $
!
! 1320 2014-03-20 08:40:49Z raasch
! kind-parameters added to all INTEGER and REAL declaration statements, 
! kinds are defined in new module kinds, 
! old module precision_kind is removed,
! revision history before 2012 removed,
! comment fields (!:) to be used for variable explanations added to
! all variable declaration statements 
!
! 1046 2012-11-09 14:38:45Z maronga
! added preprocessor directive for parameter file check 
! 
! 1036 2012-10-22 13:43:42Z raasch
! code put under GPL (PALM 3.9)
!
! 211 2008-11-11 04:46:24Z raasch
! Former file user_interface.f90 split into one file per subroutine
!
! Description:
! ------------
! Calculation of user-defined statistics, i.e. horizontally averaged profiles
! and time series.
! This routine is called for every statistic region sr defined by the user,
! but at least for the region "total domain" (sr=0).
! See section 3.5.4 on how to define, calculate, and output user defined
! quantities.
!------------------------------------------------------------------------------!

    USE arrays_3d
    
    USE indices
    
    USE kinds
    
    USE netcdf_control
    
    USE pegrid
    
    USE statistics
    
    USE user

    IMPLICIT NONE

    CHARACTER (LEN=*) ::  mode   !: 

    INTEGER(iwp) ::  i    !: 
    INTEGER(iwp) ::  j    !: 
    INTEGER(iwp) ::  k    !: 
    INTEGER(iwp) ::  sr   !: 
    INTEGER(iwp) ::  tn   !: 

    REAL(wp),                                                                  &
       DIMENSION(dots_num_palm+1:dots_max) ::                                  &
          ts_value_l   !: 


    IF ( mode == 'profiles' )  THEN

!
!--    Sample on how to calculate horizontally averaged profiles of user-
!--    defined quantities. Each quantity is identified by the index
!--    "pr_palm+#" where "#" is an integer starting from 1. These
!--    user-profile-numbers must also be assigned to the respective strings
!--    given by data_output_pr_user in routine user_check_data_output_pr.
!       !$OMP DO
!       DO  i = nxl, nxr
!          DO  j = nys, nyn
!             DO  k = nzb_s_inner(j,i)+1, nzt
!!
!!--             Sample on how to calculate the profile of the resolved-scale
!!--             horizontal momentum flux u*v*
!                sums_l(k,pr_palm+1,tn) = sums_l(k,pr_palm+1,tn) +               &
!                      ( 0.5 * ( u(k,j,i) + u(k,j,i+1) ) - hom(k,1,1,sr) ) *     &
!                      ( 0.5 * ( v(k,j,i) + v(k,j+1,i) ) - hom(k,1,2,sr) )       &
!                                                 * rmask(j,i,sr)
!!
!!--             Further profiles can be defined and calculated by increasing
!!--             the second index of array sums_l (replace ... appropriately)
!                sums_l(k,pr_palm+2,tn) = sums_l(k,pr_palm+2,tn) + ...           &
!                                         * rmask(j,i,sr)
!             ENDDO
!          ENDDO
!       ENDDO

    ELSEIF ( mode == 'time_series' )  THEN

!
!--    Sample on how to add values for the user-defined time series quantities.
!--    These have to be defined before in routine user_init. This sample
!--    creates two time series for the absolut values of the horizontal
!--    velocities u and v.
!       ts_value_l = 0.0
!       ts_value_l(dots_num_palm+1) = ABS( u_max )
!       ts_value_l(dots_num_palm+2) = ABS( v_max )
!
!--     Collect / send values to PE0, because only PE0 outputs the time series.
!--     CAUTION: Collection is done by taking the sum over all processors.
!--              You may have to normalize this sum, depending on the quantity
!--              that you like to calculate. For serial runs, nothing has to be
!--              done.
!--     HINT: If the time series value that you are calculating has the same
!--           value on all PEs, you can omit the MPI_ALLREDUCE call and
!--           assign ts_value(dots_num_palm+1:,sr) = ts_value_l directly.
!#if defined( __parallel ) && ! defined ( __check )
!       IF ( collective_wait )  CALL MPI_BARRIER( comm2d, ierr )
!       CALL MPI_ALLREDUCE( ts_value_l(dots_num_palm+1),                         &
!                           ts_value(dots_num_palm+1,sr),                        &
!                           dots_max-dots_num_palm, MPI_REAL, MPI_SUM, comm2d,   &
!                           ierr )
!#else
!       ts_value(dots_num_palm+1:,sr) = ts_value_l
!#endif

    ENDIF

 END SUBROUTINE user_statistics