Generalised Hypergeometric (pFq) function

[andrjohns]

Description

One of the pre-requisites for implementing the inverse-CDF (quantile) of the Gamma distribution is the hypergeometric 2F2 function, which is needed for the gradients.

The gradients are the same for the 2F2 and the generalised pFq, so may as well implement the more generalised version

Current Version:

v4.1.0

[sethaxen]

Was this completed by #2510?

[sethaxen]

Also @andrjohns is this the last major prerequisite for implementing the Gamma quantile and its derivative?

[nikunj410]

Hi @andrjohns, I am working on the N-mixture model to estimate abundance from count data. The model relies on the hypergeometric_2F2 and hypergeometric_3F2 functions. Has/will these functions be implemented/exposed in stan?

Thank you