multinom2poisson {fastTopics}

Recover Poisson NMF Fit from Multinomial Topic Model Fit

Description

This function recovers parameter estimates of the Poisson non-negative matrix factorization (NMF) given parameter estimates for a multinomial topic model.

Usage

multinom2poisson(fit, X)

Arguments

fit

An object of class “multinom_topic_model_fit”, such as an output from poisson2multinom. If a Poisson NMF fit is provided (that is, an object of class “poisson_nmf_fit”), the fit object is immediately returned “as is”.

X

Optional n x m matrix of counts, or pseudocounts. It can be a sparse matrix (class "dgCMatrix") or dense matrix (class "matrix"). This only needs to be provided if the document sizes fit$s are not available.

Value

The return value is the list fit, in which matrices fit$F and fit$L specify the factors and loadings in the Poisson non-negative matrix factorization; specifically, the counts matrix is modeled by the low-rank matrix product tcrossprod(fit$L,fit$F).