@Override
    public double entropy() {
        return Math.log(scale) + 2;
    }
@Test
    public void testEntropy() {
        System.out.println("entropy");
        LogisticDistribution instance = new LogisticDistribution(2.0, 1.0);
        instance.rand();
        assertEquals(2.0, instance.mean(), 1E-7);
    }