Calculate the Normalizing Constant in log scale for COM-Poisson distribution

Source: R/Z.R

A function to approximate the normalizing constant for COM-Poisson distributions via truncation. The standard COM-Poisson parametrization is being used here.

logZ(log_lambda, nu, summax = 100)

Arguments

log_lambda

rate parameter in log scale.

nu

dispersion parameter, straightly positive.

summax

maximum number of terms to be considered in the truncated sum.

Details

As of version 0.2.0 of this package, logZ will supersede Z for calculating the normalizing constant. logZ utilised a method that can calculate log(exp(logx) + exp(logy)) in a somewhat numerically stable way.

This function was originally purposed in the cmpreg package of Ribeiro Jr, Zeviani & Demétrio (2019).

References

Ribeiro Jr, E. E., Zeviani, W. M., Demétrio, C. G. B. (2019) cmpreg: Reparametrized COM-Poisson Regression Models. R package version 0.0.1.