Matrice_SuperMorse.cpp

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#include <Matrice_SuperMorse.h>
 
/*! @brief Computes "resu += MATRICE * x" and a dot product (this is a building block for the conjugate gradient, see class Solv_GCP)
 *
 *  Return value:
 *    local contribution of this processor to "(MATRICE * x) dot x"
 *    (note: the dot product counts all rows of the matrix;
 *      shared items are not removed!)
 *    (note: this is different from resu dot x!)
 *
 */
double Matrice_SuperMorse::ajouter_mult_vect_et_prodscal(const DoubleVect& x, DoubleVect& resu) const
{
  assert(resu.size() == x.size());
 
  const int nb_lignes = lignes_non_vides_.size_array();
  const int *tab_lignes = lignes_non_vides_.addr();
  // The first index of tab1_ we care about is the second element of the array
  // (the first element is always 1)
  assert(tab1_[0] == 1);
  const auto *tab1_ptr = tab1_.addr() + 1;
  assert(tab1_.size_array() == nb_lignes + 1);
  const int *tab2_ptr = tab2_.addr();
  const double *coeff_ptr = coeff_.addr();
  const double *x_ptr = x.addr() - 1; // offset by 1 because we index with Fortran indices
  double *resu_ptr = resu.addr() - 1; // same
  int n = 1; // index of the current coefficient in tab2 and coeff
 
  double prod_scal_local = 0;
 
  for (int i = 0; i < nb_lignes; i++)
    {
      // Row index in the matrix:
      const int i_ligne = *(tab_lignes++);
      assert(i_ligne >= 1 && i_ligne <= resu.size_array());
      double r = 0.;
      // End index of the coefficients for this row in tab2 and coeff
      const auto n_fin = *(tab1_ptr++);
      for (; n < n_fin; n++)
        {
          const int colonne = *(tab2_ptr++);
          assert(colonne >= 1 && colonne <= x.size_array());
          const double coef = *(coeff_ptr++);
          const double xb = x_ptr[colonne];
          r += coef * xb;
        }
      resu_ptr[i_ligne] += r;
      // note: we only want to compute the dot product between x and the part added to resu
      //  (not with the existing values of resu before the call)
      prod_scal_local += r * x_ptr[i_ligne];
    }
  return prod_scal_local;
}