public static double pow2(double x) {
        return x * x;
    }
@Test
    public void testPow2() {
        System.out.println("pow2");
        assertEquals(0, MathEx.pow2(0), 1E-10);
        assertEquals(1, MathEx.pow2(1), 1E-10);
        assertEquals(4, MathEx.pow2(2), 1E-10);
        assertEquals(9, MathEx.pow2(3), 1E-10);
    }