# 23 Simplex Distributions

The simplex probabilities have support on the unit $$K$$-simplex for a specified $$K$$. A $$K$$-dimensional vector $$\theta$$ is a unit $$K$$-simplex if $$\theta_k \geq 0$$ for $$k \in \{1,\ldots,K\}$$ and $$\sum_{k = 1}^K \theta_k = 1$$.