train_iPoiss: Train an independent Poisson model
In gregorp90/RStan-package-test: Copula-Based Factor Analysis

This function trains an independent Poisson model for multivariate count estimation.

1	train_iPoiss(train, gp_train)

`train`	data frame. The training data set, consisting of counts. Columns represent variables, rows represent observations.
`gp_train`	vector. Groups for each observation.

A list.

`params`	A matrix of Poisson parameters for each group-variable combination. Rows represent groups, columns represent variables.
`train`	Train data set.
`gp_train`	Groups of the train data set.