Dirichlet Distribution

The Dirichlet distribution is often known as the multi-class (or multivariate) generalization of the Beta Distribution. In contrast to the Beta distribution, which provides a probability draw for one class, the Dirichlet distribution generalizes this to multi-class.

Beta Distribution

The Beta distribution is a Probability distribution that has support over the interval $[0, 1]$. It's most commonly used to express degree of belief in the value of a probability term.

Dirichlet Process

What exactly is a Dirichlet process?

We start from the Dirichlet Distribution, which provides a vector of probabilities over states. The vector of probabilities must sum to 1, and they give Categorical Distribution probabilities, i.e. the probability of getting a draw from that category.

In contrast to the Dirichlet distribution, which has a fixed number of categories, the Dirichlet process describes a generative process for an infinite number of categories. There are a few algorithmic variants of the Dirichlet process, including the Chinese Restaurant Process, the Indian Buffet Process, and the Stick Breaking Process.

In practice, when computing with Dirichlet processes, we tend to use the Stick Breaking Process with a large but finite number of states.