public static double sd(int[] array) {
        return sqrt(var(array));
    }
@Test
    public void testSd() {
        System.out.println("sd");
        double[] data = {1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0, 9.0};
        assertEquals(2.73861, MathEx.sd(data), 1E-5);
    }