From: <rdpeng_at_gmail.com>

Date: Thu 27 Jul 2006 - 17:53:16 GMT

Date: Thu 27 Jul 2006 - 17:53:16 GMT

Technically speaking, your version of R is from the previous century. You might
want to check with a more recent version before reporting a bug.

-roger

dolive@math.siu.edu wrote:

> The R poisson random generator rpois appears to have a bug for

*> theta 10 or larger. The sample mean of the pseudo variates is too
**> small: sample mean approx theta - 0.5.
**>
**> I use Version 1.1.1 (August 15, 2000) Of R on a Dell OptiPlex computer
**> with the
**> Windows XP Professional operating system.
**>
**> Has this bug been fixed in later versions?
**>
**> (I found another reported rpois bug, but it appears to be different
**> and to have been fixed :
**>
**> rpois gives a large number repeatedly
**> kjetikj@astro.uio.no
**> Tue, 15 Feb 2000 12:18:28 +0100 (MET))
**>
**>
**>
**> The following output helps illustrate the bug.
**>
**> > zsim
**> function(nc = 100, nr = 500, theta = 1)
**> {# check rpois function
**> x <- matrix(rpois(nr*nc, theta),nrow=nr,ncol=nc)
**> z<-apply(x,2,mean)
**> list(z=z)}
**>
**> > zsim(theta=10)
**> $z
**> [1] 9.594 9.552 9.538 9.448 9.438 9.544 9.630 9.474 9.568 9.700 9.720 9.642
**> [13] 9.624 9.328 9.420 9.492 9.368 9.674 9.528 9.436 9.296 9.502 9.260 9.440
**> [25] 9.572 9.698 9.372 9.458 9.532 9.570 9.534 9.528 9.572 9.536 9.234 9.416
**> [37] 9.400 9.370 9.438 9.628 9.672 9.738 9.454 9.478 9.438 9.496 9.672 9.308
**> [49] 9.632 9.386 9.842 9.452 9.632 9.460 9.660 9.688 9.486 9.492 9.576 9.664
**> [61] 9.290 9.300 9.304 9.472 9.618 9.480 9.458 9.558 9.782 9.532 9.198 9.258
**> [73] 9.384 9.630 9.520 9.646 9.554 9.406 9.390 9.554 9.610 9.382 9.604 9.638
**> [85] 9.304 9.586 9.848 9.434 9.460 9.644 9.450 9.542 9.502 9.446 9.828 9.364
**> [97] 9.664 9.628 9.704 9.354
**>
**> Notice that all 100 sample means of size 500 are less than 10, about
**> half should be larger.
**>
**> The following commands also suggest that the rpois function is biased
**> for theta > 10.
**>
**> > hist(zsim(theta=1)$z)
**> > hist(zsim(theta=10)$z)
**> > hist(zsim(theta=100)$z)
**> > hist(zsim(theta=1000)$z)
**>
**>
**> Best Regards,
**>
**>
**> David Olive
**> dolive@math.siu.edu
**>
**> ______________________________________________
**> R-devel@r-project.org mailing list
**> https://stat.ethz.ch/mailman/listinfo/r-devel
**>
*

-- Roger D. Peng | http://www.biostat.jhsph.edu/~rpeng/ ______________________________________________ R-devel@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-develReceived on Fri Jul 28 04:01:42 2006

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