[Rd] Bug report: Function ppois(0:20, lambda=0.9) does not generate a non-decreasing result.

Serguei Sokol @okol @ending from in@@-toulou@e@fr
Wed Dec 5 10:08:47 CET 2018


Le 04/12/2018 à 19:12, Martin Maechler a écrit :
>>>>>> Serguei Sokol
>>>>>>      on Tue, 4 Dec 2018 11:46:32 +0100 writes:
>      > Le 04/12/2018 à 11:27, Iñaki Ucar a écrit :
>      >> On Tue, 4 Dec 2018 at 11:12, <qweytr1 using mail.ustc.edu.cn> wrote:
>      >>> function ppois is a function calculate the CDF of Poisson distribution, it should generate a non-decreasing result, but what I got is:
>      >>>
>      >>>> any(diff(ppois(0:19,lambda=0.9))<0)
>      >>> [1] TRUE
> ...
>      > any(diff(exp(ppois(0:19, lambda=0.9, log.p=TRUE))) < 0)
>      > #[1] FALSE
>
>      > But may be there is another, more economic way?
>
> Well, log probabilites *are* very economic for many such p*()
> functions.
I have not doubt about it. My "economic way" was related to get ppois() 
*non decreasing*, at least, more economic than exp-log.p trick.

Serguei.



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