const gsl_matrix *covariance_moments (const struct covariance *cov, int m);
const struct categoricals * covariance_get_categoricals (const struct covariance *cov);
+struct interaction;
+void covariance_get_interaction_indices (const struct covariance *cov, const struct interaction **iacts);
void covariance_get_var_indices (const struct covariance *cov, const struct variable **vars);
size_t covariance_dim (const struct covariance * cov);