# Rev Language Reference

## dnDirichlet - Dirichlet Distribution

Dirichlet probability distribution on a simplex.

### Usage

dnDirichlet(RealPos[] alpha)

### Arguments

 alpha : RealPos[] (pass by const reference) The concentration parameter.

### Details

The Dirichlet probability distribution is the generalization of the Beta distribution. A random variable from a Dirichlet distribution is a simplex, i.e., a vector of probabilities that sum to 1.

### Example

# lets get a draw from a Dirichlet distribution
a <- [1,1,1,1]   # we could also use rep(1,4)
b ~ dnDirichlet(a)
b
# let check if b really sums to 1
sum(b)