From hothorn@ci.tuwien.ac.at  Fri Mar 24 13:40:13 2000
From: hothorn@ci.tuwien.ac.at (Torsten Hothorn)
Date: Fri, 24 Mar 2000 14:40:13 +0100 (CET)
Subject: [Rd] quantiles of the hypergeometric distribution (PR#502)
In-Reply-To: <200003241223.NAA02113@pubhealth.ku.dk>
Message-ID: <Pine.LNX.4.21.0003241433160.21466-100000@boromir.ci.tuwien.ac.at>


> Hello!
> 
> I use R-version 1.0.0
> To get the 0.95 quantile of the hypergeometric
> distribution with the parameters m=45000,n=5000 and
> k=600 I use the R-command 
> 
> > qhyper(0.95,45000,5000,600).
> 
> 
> The value obtained is 600. However, the true value
> is 552. 

Well, 

had a short look. The problem arises in qhyper.c at line 56:

 term = exp(lfastchoose(NR, xr) + lfastchoose(NB, xb) - lfastchoose(N, n));

The expression inside the exp() function gives -1415.411856 and exp()
returns 0. So term and sum in 

 while(sum < p && xr < xend) {
        xr++;
        NB++;
        term *= (NR / xr) * (xb / NB);
        sum += term;
        xb--;
        NR--;
    }

are 0 all the time and xend = 600 is returned. 

R-Core: How to fix this?

Torsten

*****************************************************************
*				                                *
* Torsten Hothorn, Statistician 		                *
* at the moment: Institut fuer Statistik, TU Wien	        *
* Tel: 0043 1 58801 10772                  			*
* Fax: 0043 1 58801 10798                                       *
*                                                               *
*****************************************************************


-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-
r-devel mailing list -- Read http://www.ci.tuwien.ac.at/~hornik/R/R-FAQ.html
Send "info", "help", or "[un]subscribe"
(in the "body", not the subject !)  To: r-devel-request@stat.math.ethz.ch
_._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._


[Rd] quantiles of the hypergeometric distribution (PR#502)
Torsten Hothorn