+/*
+ Return or set the standard deviation of the independent variable.
+ */
+double pspp_linreg_get_indep_variable_sd (pspp_linreg_cache *, const struct variable *);
+void pspp_linreg_set_indep_variable_sd (pspp_linreg_cache *, const struct variable *, double);
+/*
+ Mean of the independent variable.
+ */
+double pspp_linreg_get_indep_variable_mean (pspp_linreg_cache *, const struct variable *);
+void pspp_linreg_set_indep_variable_mean (pspp_linreg_cache *, const struct variable *, double);
+
+/*
+ Regression using only the covariance matrix.
+ */
+void pspp_linreg_with_cov (const struct covariance_matrix *, pspp_linreg_cache *);
+double pspp_linreg_mse (const pspp_linreg_cache *);