 Poisson-Dirichlet distribution

The Poisson-Dirichlet family consists of laws of decreasing random mass partitions $(p_i)$ with ${\sum }_i{p}_i=1$. Its two-parameter notation is $PD(\alpha ,\theta )$, with $0\le \alpha <1$ and $\theta >-\alpha$. The conventional one-parameter probability distribution $PD(\theta )$ means $PD(0,\theta )$, for $\theta >0$, and can be constructed from normalized gamma jumps.