void design_matrix_set_case_count (struct design_matrix *, const struct variable *, size_t);
size_t design_matrix_get_case_count (const struct design_matrix *, const struct variable *);
void design_matrix_set_case_count (struct design_matrix *, const struct variable *, size_t);
size_t design_matrix_get_case_count (const struct design_matrix *, const struct variable *);