test_omp.cc

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/* Copyright (C) 2013 Oliver Lemke
 
 This program 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 2, or (at your option) any
 later version.
 
 This program 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 this program; if not, write to the Free Software
 Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307,
 USA. */
 
#include <iostream>
#include "matpackIV.h"
#include "arts_omp.h"
#include "rte.h"
 
int main()
{
    Index nloop = 2000;
    Index nf = 115;
    Index np = 50;
    Index stokes_dim = 1;
 
    Tensor4 ppath_abs(nf, stokes_dim, stokes_dim, np, 0.);
    Tensor4 trans_cumulat(nf, stokes_dim, stokes_dim, np, 0.);
    Tensor4 trans_partial(nf, stokes_dim, stokes_dim, np, 0.);
    Vector scalar_tau(nf, 0.);
    Vector lstep(np, 1.);
 
 
    ArrayOfArrayOfIndex extmat_case(np);
    for( Index ip = 0; ip < np; ip++)
    {
        extmat_case[ip].resize(nf);
    }
 
// Commenting in the next two lines shouldn't change anything, because
// the outer loop will still run sequentially and the inner one parallel.
// Nonetheless, performance grinds to a halt because OpenMP can not reuse
// the initial threads. It has to create new ones for the inner loop on
// every iteration.
/*#pragma omp parallel for \
if (0)*/
    for( Index n = 0; n < nloop; n++)
    {
        for( Index ip = 1; ip < np; ip++)
        {
#pragma omp parallel for
            for( Index iv=0; iv<nf; iv++ )
            {
                // Transmission due to absorption
                Matrix ext_mat(stokes_dim,stokes_dim);
                for( Index is1=0; is1<stokes_dim; is1++ ) {
                    for( Index is2=0; is2<stokes_dim; is2++ ) {
                        ext_mat(is1,is2) = 0.5 * ( ppath_abs(iv,is1,is2,ip-1) +
                                                  ppath_abs(iv,is1,is2,ip  ) );
                    }
                }
                scalar_tau[iv] += lstep[ip-1] * ext_mat(0,0);
                extmat_case[ip-1][iv] = 0;
                ext2trans( trans_partial(iv,joker,joker,ip-1),
                          extmat_case[ip-1][iv], ext_mat, lstep[ip-1] );
 
                // Cumulative transmission
                // (note that multiplication below depends on ppath loop order)
                mult( trans_cumulat(iv,joker,joker,ip),
                     trans_cumulat(iv,joker,joker,ip-1),
                     trans_partial(iv,joker,joker,ip-1) );
            }
        }
    }
    return 0;
}