[R] strange behaviour of negative binomial

[Gabor Grothendieck]

I tried it on Windows XP under both 2.0.1 and 2.1.0 and it seemed to
work both times.  I issued the command:  

set.seed(1)

before both runs to ensure that I was actually using the same
random numbers.  I suggest you try that in all your runs too just 
in case its a problem with some sets of random numbers but not 
others.


dax42 <Dax42 <at> web.de> writes:

: 
: 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
: >
: 
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