@Override
    public int length() {
        return length;
    }
@Test
    public void testLength() {
        System.out.println("length");
        MultivariateGaussianDistribution instance = new MultivariateGaussianDistribution(mu, 1.0);
        assertEquals(4, instance.length());

        instance = new MultivariateGaussianDistribution(mu, sigma[0]);
        assertEquals(6, instance.length());

        instance = new MultivariateGaussianDistribution(mu, Matrix.of(sigma));
        assertEquals(9, instance.length());
    }