Hi All,

I’m trying to estimate a mixture of latent variables, but I’m having trouble parameterising the mixing proportions.

In these models, for identification the factor mean in one class is fixed to zero (i.e. a reference class) and the factor means in the other classes are freely estimated. The mixing proportions are then parameterised as the probability of belonging to a given class over the reference class.

Let’s say I begin with the ‘raw’ mixing proportions:

```
parameters {
simplex[K] theta;
...
}
model {
theta ~ dirichlet(rep_vector(10,K));
...
}
```

How would I transform these to the probabilities that I need? My intuition would be `softmax(theta - theta[K])`

, but I’m not sure if that’s what I’m after.

Thanks!

Andrew