public static LinearModel fit(Formula formula, DataFrame data) {
        return fit(formula, data, new Properties());
    }
@Test
    public void testProstate() {
        System.out.println("Prostate");

        LinearModel model = OLS.fit(Prostate.formula, Prostate.train);
        System.out.println(model);

        double[] prediction = model.predict(Prostate.test);
        double rmse = RMSE.of(Prostate.testy, prediction);
        System.out.println("RMSE on test data = " + rmse);
        assertEquals(0.721993, rmse, 1E-4);
    }