public static int[][] clone(int[][] x) {
        int[][] matrix = new int[x.length][];
        for (int i = 0; i < x.length; i++) {
            matrix[i] = x[i].clone();
        }

        return matrix;
    }
@Test
    public void testClone() {
        System.out.println("clone");
        double[][] A = {
            {0.7220180, 0.07121225, 0.6881997},
            {-0.2648886, -0.89044952, 0.3700456},
            {-0.6391588, 0.44947578, 0.6240573}
        };

        double[][] B = MathEx.clone(A);

        assertTrue(MathEx.equals(A, B));
        assertNotSame(A, B);
        for (int i = 0; i < A.length; i++) {
            assertNotSame(A[i], B[i]);
        }
    }