Dirichlet regression

[stemangiola]

In the meanwhile, I have two questions.

1. Why the gamma representation should be better than the “beta regression”

@stemangiola

matrix[P,S] mu;
mu = inv_logit( alpha * x’);
to_vector(y) ~ beta(to_vector(mu) * phi, (1 - to_vector(mu)) * phi);

2. How come something quite common such as softmax/dirichlet regression has never been encountered/established in stan-like languages?