@Override
    public double rand() {
        if (rng == null) {
            rng = new RejectionLogLogistic();
        }

        return rng.rand();
    }
@Test
    public void testSd() {
        System.out.println("sd");
        BetaDistribution instance = new BetaDistribution(2, 5);
        instance.rand();
        assertEquals(0.1597191, instance.sd(), 1E-7);
    }