@Override
    public double entropy() {
        return (dim * LOG2PIE + Math.log(sigmaDet)) / 2;
    }
@Test
    public void testEntropy() {
        System.out.println("entropy");
        MultivariateGaussianDistribution instance = new MultivariateGaussianDistribution(mu, Matrix.of(sigma));
        assertEquals(2.954971, instance.entropy(), 1E-6);
    }