public static double mean(int[] array) {
        return (double) sum(array) / array.length;
    }
@Test
    public void testMean_doubleArr() {
        System.out.println("mean");
        double[] data = {1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0, 9.0};
        assertEquals(5, MathEx.mean(data), 1E-6);
    }