col = design_matrix_var_to_column ((const struct design_matrix *) dm, var);
assert (col != DM_COLUMN_NOT_FOUND);
gsl_matrix_set (dm->m, row, col, val->f);
col = design_matrix_var_to_column ((const struct design_matrix *) dm, var);
assert (col != DM_COLUMN_NOT_FOUND);
gsl_matrix_set (dm->m, row, col, val->f);