    @Test
    public void testIdentity()
    {

        final Vector2VectorFunc testFunc = (x, arg) -> x;

        final double[] inputArr = new double[]{-1, -1, 2, 4, 5, 6, 8};
        final double[][] fprime = Jacobian.approxJacobian(inputArr, testFunc);

        for (int i = 0; i < fprime.length; i++)
        {
            for (int j = 0; j < fprime[0].length; j++)
            {
                if (i == j)
                {
                    assertTrue(Math.abs(fprime[i][j] - 1) < TestUtil.ERROR);
                }
                else
                {
                    assertTrue(Math.abs(fprime[i][j] - 0) < TestUtil.ERROR);
                }
            }
        }
    }