public static float norm(float[] x) {
        return norm2(x);
    }
@Test
    public void testNorm_doubleArr() {
        System.out.println("norm");
        double[] x = {-2.1968219, -0.9559913, -0.0431738, 1.0567679, 0.3853515};
        assertEquals(2.647086, MathEx.norm(x), 1E-6);
    }