public static QDA fit(double[][] x, int[] y) {
        return fit(x, y, null, 1E-4);
    }
@Test
    public void testIris() throws Exception {
        System.out.println("Iris");

        ClassificationMetrics metrics = LOOCV.classification(Iris.x, Iris.y, QDA::fit);

        System.out.println(metrics);
        assertEquals(0.9733, metrics.accuracy, 1E-4);

        QDA model = QDA.fit(Iris.x, Iris.y);
        java.nio.file.Path temp = Write.object(model);
        Read.object(temp);
    }