# [Rd] lambda==0 in dpois() (PR#459)

**Peter Dalgaard BSA
**
p.dalgaard@biostat.ku.dk

*25 Feb 2000 20:46:40 +0100*

bolker@zoo.ufl.edu writes:
>* The nice new log=TRUE option in dpois appears to mess up the
*>* case where lambda=0 (I was trying to calculate the likelihood
*>* of a saturated model). Because the behavior is now always to
*>* calculate the probability in terms of exp(log(prob)), there's
*>* a test for lambda<=0 which really needs to be only lambda<0.
*>*
*>* dpois(0:5,0)
*>*
*>* ought to give
*>*
*>* 1 0 0 0 0
*>*
*>* but gives NaNs instead.
*>*
*>* Here's a patch to src/nmath/dpois.c that appears to work (although it could ? be more
*>* elegant).
*
Thanks. We may just be able to squeeze that one in before 1.0.0. But
shouldn't it return -Inf (ML_NEGINF) for the log case rather than NaN?
--
O__ ---- Peter Dalgaard Blegdamsvej 3
c/ /'_ --- Dept. of Biostatistics 2200 Cph. N
(*) \(*) -- University of Copenhagen Denmark Ph: (+45) 35327918
~~~~~~~~~~ - (p.dalgaard@biostat.ku.dk) FAX: (+45) 35327907
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