void covariance_accumulate_pass2 (struct covariance *, const struct ccase *);
gsl_matrix * covariance_calculate (struct covariance *);
-gsl_matrix * covariance_calculate_unnormalized (struct covariance *);
+const gsl_matrix * covariance_calculate_unnormalized (struct covariance *);
void covariance_destroy (struct covariance *cov);