From gb@stat.umu.se  Fri Apr  3 08:20:07 1998
From: gb@stat.umu.se (Goran Brostrom)
Date: Fri, 3 Apr 1998 09:20:07 +0200 (MET DST)
Subject: R-beta: Bug in dhyper (and phyper) (fwd)
Message-ID: <Pine.GSO.3.95.980403091231.24285A-100000@pc30.stat.umu.se>


Last night I sent the bug report below to r-help. I have since then looked
at dhyper.c and found:

        if (NR < 0 || NB < 0 || n <= 0 || n > N)
                DOMAIN_ERROR;

I changed 'n <= 0' to 'n < 0' and then dhyper worked as I wanted. Am I
introducing some potentially dangerous behaviour by this change?

Goran
----------------------------------------------------------------------
I think I have found a bug in the function dhyper (R-0.61.2):

R> dhyper(0,3,3,0)
Warning: NAs produced in function "dhyper"
[1] NA

Documentation:

"Usage

dhyper(x, N1, N2, n)

.......

The hypergeometric distribution is used for sampling without replacement. 
It has density 

  p(x) = Choose(N1, x) Choose(N2, n-x) / Choose(N1+N2, n)

for x = 0,...,n"

R> choose(3,0) * choose(3,0) / choose(6,0)
[1] 1

This result is correct, and obviously dhyper is implemented in some way 
not consistent with the documentation.

Also note the spelling error of 'choose' in the documentation.

---
Goran Brostrom                         phone : +46 90 7865223
Department of Statistics                              7865213 (secr)
Umea University                        fax   :        7866614
S-90187 Umea, Sweden                   e-mail: gb@stat.umu.se

-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-
r-help 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-help-request@stat.math.ethz.ch
_._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._


-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-
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
_._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._


R-beta: Bug in dhyper (and phyper) (fwd)
Goran Brostrom