- tmp = gsl_matrix_get (cov->m, row, col);
- gsl_matrix_set (cov->m, row, col, (val2->f - mean) * x + tmp);
- gsl_matrix_set (cov->m, col, row, (val2->f - mean) * x + tmp);
+ tmp = design_matrix_get_element (cov, row, col);
+ design_matrix_set_element (cov, row, col, (val2->f - mean) * x + tmp);
+ design_matrix_set_element (cov, col, row, (val2->f - mean) * x + tmp);