[R] strange behaviour of negative binomial

[dax42]

Hi,

I am sorry for the incorrect terms. Of course I mean the cumulative 
distribution functions.
As I just got two answers telling me my problem does not exist, I tried 
again on a different setup - and indeed it works.

So, my first run was done on a Mac OS X 10.3.7 running R 2.0.0, GUI 
version.
Now I tried it on the same system, only I used the R 2.0.0 on my X11, 
not the GUI version.

First setup produces the error (and is VERY slow, talking about several 
minutes here...)
Second works fine.

Does anybody have a similar setup and could try this out as well?
Thanks!
Dax

Am 05.01.2005 um 23:32 schrieb Peter Dalgaard:

> dax42 <Dax42 at web.de> writes:
>
>> Dear list,
>>
>> I ran into a strange behaviour of the pnbinom function - or maybe I
>> just made a stupid mistake.
>> First thing is that pnbinom seems to be very slow. The other - more
>> interesting one - is that I get two different curves when I plot the
>> estimated density and the density given by pnbinom. Shouldn't it be
>> the same?
>> This is only the case, I think, if I use the parameter size = 1. I
>> just tried it for size = 2 and the result seemed correct..
>>
>> Anyways, this is what I tried:
>>
>> #parameters
>> proba<-0.001039302;
>> s<-1;
>>
>> #random numbers with this distribution
>> dom<-rnbinom(10000,s,proba);
>>
>> #first plot
>> plot(ecdf(dom),do.points=FALSE);
>>
>> #second plot
>> x<-seq(0,8700,0.5);
>> lines(x,pnbinom(x,s,proba),col="red");
>
> Errrr... What's the problem here? The two curves look quite similar to
> me. (And both are of course cumulative distribution functions and not
> densities, but it doesn't sound like that is the problem.)
>
> -- 
>    O__  ---- Peter Dalgaard             Blegdamsvej 3
>   c/ /'_ --- Dept. of Biostatistics     2200 Cph. N
>  (*) \(*) -- University of Copenhagen   Denmark      Ph: (+45) 35327918
> ~~~~~~~~~~ - (p.dalgaard at biostat.ku.dk)             FAX: (+45) 35327907
>