A function to approximate the normalizing constant for COM-Poisson distributions
via truncation. The standard COM-Poisson parametrization is being used here.
Notice that the sum is hard coded to truncate at 100 so the approximation will be quite
bad if the COM-Poisson has a large rate or mean.
Usage
Z(lambda, nu, log.z = FALSE, summax)
Arguments
- lambda
rate parameter, straightly positive
- nu
dispersion parameter, straightly positive
- log.z
logical; if TRUE, normalising constant \(Z\) are returned as
\(log(Z)\).
- summax
maximum number of terms to be considered in the truncated sum
Value
A numeric vector giving the (approximate) COM-Poisson normalizing
constant \(Z(\lambda, \nu)\) (or its natural log if log.z = TRUE),
recycled to the length of the longer of lambda and nu.
