The documentation states : An alternative parametrization (often used in ecology) is by the mean ‘mu’, and ‘size’, the dispersion parameter.
However, this fails : > rnbinom(10, mu = 100, size = 0) [1] NaN NaN NaN NaN NaN NaN NaN NaN NaN NaN Warning message: In rnbinom(10, mu = 100, size = 0) : NAs produced For dispersion set to 0, it should work like drawing from a Poisson distribution. It also produces incorrect draws for non-zero dispersions : > rnbinom(10, mu = 100, size = 0.000001) [1] 0 0 0 0 0 0 0 0 0 0 It also fails for underdispersed count models : > rnbinom(10, mu = 100, size = -0.1) [1] NaN NaN NaN NaN NaN NaN NaN NaN NaN NaN Warning message: In rnbinom(10, mu = 100, size = -0.1) : NAs produced > sessionInfo() R version 3.0.2 (2013-09-25) Platform: x86_64-pc-linux-gnu (64-bit) locale: [1] LC_CTYPE=en_AU.UTF-8 LC_NUMERIC=C [3] LC_TIME=en_AU.UTF-8 LC_COLLATE=en_AU.UTF-8 [5] LC_MONETARY=en_AU.UTF-8 LC_MESSAGES=en_AU.UTF-8 [7] LC_PAPER=en_AU.UTF-8 LC_NAME=C [9] LC_ADDRESS=C LC_TELEPHONE=C [11] LC_MEASUREMENT=en_AU.UTF-8 LC_IDENTIFICATION=C attached base packages: [1] stats graphics grDevices utils datasets methods base loaded via a namespace (and not attached): [1] tools_3.0.2 -------------------------------------- Dario Strbenac PhD Student University of Sydney Camperdown NSW 2050 Australia ______________________________________________ R-devel@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-devel
