[R] Strange means of numbers drawn from rpois

ben@zoo.ufl.edu ben at zoo.ufl.edu
Wed Nov 8 17:06:43 CET 2000

  Happens on linux RH 6.0 R-1.1.1 as well, and furthermore a brief poke
into src/nmath/rpois.c shows that it's using a different method for
lambda>=10, so there's reason to believe there's a fairly localized (but
scary!!!) bug.  I can't really understand/find/fix it, without a lot more
work and looking up the original reference (the rejection method given in
_Numerical Recipes_ is quite different) ...

 I'd say the following is a pretty clear indication of a bug ...

> mean(rpois(100000,9.99))
[1] 10.00021
> mean(rpois(100000,10.0))
[1] 9.50424

318 Carr Hall                                bolker at zoo.ufl.edu
Zoology Department, University of Florida    http://www.zoo.ufl.edu/bolker
Box 118525                                   (ph)  352-392-5697
Gainesville, FL 32611-8525                   (fax) 352-392-3704

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