reorder_columns()

void F4GB::reorder_columns ( )

private

Definition at line 322 of file f4.cpp.

{
  // Set up to sort the columns.
  // Result is an array 0..ncols-1, giving the new order.
  // Find the inverse of this permutation: place values into "ord" column
  // fields.
  // Loop through every element of the matrix, changing its comp array.
 
  int nrows = INTSIZE(mat->rows);
  int ncols = INTSIZE(mat->columns);
 
  // sort the columns
 
  int *column_order = new int[ncols];
  int *ord = new int[ncols];
 
  ColumnsSorter C(mMonomialInfo, mat);
 
// Actual sort of columns /////////////////
 
  C.reset_ncomparisons();
 
  clock_t begin_time0 = clock();
  for (int i = 0; i < ncols; i++)
    {
      column_order[i] = i;
    }
 
  if (M2_gbTrace >= 2) fprintf(stderr, "ncomparisons = ");
 
  // std::cout << "-- before sort --" << std::endl;
  // show_column_info();
  
  std::stable_sort(column_order, column_order + ncols, C);
 
  // std::cout << "-- after sort --" << std::endl;  
  // show_column_info();
  
  clock_t end_time0 = clock();
  if (M2_gbTrace >= 2) fprintf(stderr, "%ld, ", C.ncomparisons0());
  double nsecs0 = (double)(end_time0 - begin_time0) / CLOCKS_PER_SEC;
  clock_sort_columns += nsecs0;
  if (M2_gbTrace >= 2) fprintf(stderr, " time = %f\n", nsecs0);

 
  for (int i = 0; i < ncols; i++)
    {
      ord[column_order[i]] = i;
    }
 
  // Now move the columns into position
  coefficient_matrix::column_array newcols;
  newcols.reserve(ncols);
  for (int i = 0; i < ncols; i++)
    {
      long newc = column_order[i];
      newcols.push_back(mat->columns[newc]);
    }
 
  // Now reset the components in each row
  for (int r = 0; r < nrows; r++)
    {
      row_elem &row = mat->rows[r];
      for (int i = 0; i < row.len; i++)
        {
          int oldcol = row.comps[i];
          int newcol = ord[oldcol];
          row.comps[i] = newcol;
        }
      for (int i = 1; i < row.len; i++)
        {
          if (row.comps[i] <= row.comps[i - 1])
            {
              fprintf(stderr, "Internal error: array out of order\n");
              break;
            }
        }
    }
 
  std::swap(mat->columns, newcols);
  delete [] column_order;
  delete [] ord;
  //Mem->components.deallocate(column_order);
  //Mem->components.deallocate(ord);
}

References clock_sort_columns, row_elem::comps, INTSIZE, row_elem::len, M2_gbTrace, mat, mMonomialInfo, ColumnsSorter::ncomparisons0(), ColumnsSorter::reset_ncomparisons(), and std::swap().

Referenced by make_matrix().