Hello, I believe a negative binomial distribution with size == Inf should behave like a Poisson distribution. Currently NaNs are returned for most input. Please find below some simple code. Thanks. Thomas # [dpqr]dnbinom(0, mu = mu, size = Inf) are undefined (NaN): mu <- 5 dnbinom(0:3, mu = mu, size = Inf) pnbinom(0:3, mu = mu, size = Inf) qnbinom(0.3, mu = mu, size = Inf) set.seed(1) rnbinom(3, mu = mu, size = Inf) # This is what should be obtained: dpois(0:3, mu) ppois(0:3, mu) qpois(0.3, mu) set.seed(1) rpois(3, mu)

Your assessment is entirely correct, thank you! I will address this.

Patch committed (svn rev 70234) a few minutes ago to R-devel. To be ported to R-patched -- for R 3.2.4 -- in two days or so. Note that rnbinom(n, size=Inf, mu=mu) will not return the same random numbers as rpois(n, mu) -- but rather the same as rnbinom(n, size=<very large>, mu=mu).