@Override
    public double p(double[] x) {
        return Math.exp(logp(x));
    }
@Test
    public void testPdf() {
        System.out.println("pdf");
        MultivariateGaussianDistribution instance = new MultivariateGaussianDistribution(mu, Matrix.of(sigma));
        for (int i = 0; i < x.length; i++) {
            assertEquals(pdf[i], instance.p(x[i]), 1E-4);
        }
    }