[Rd] bug with rpois (PR#9106)

[rdpeng at gmail.com]

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 at 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 at 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 at math.siu.edu
> 
> ______________________________________________
> R-devel at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-devel
> 

-- 
Roger D. Peng  |  http://www.biostat.jhsph.edu/~rpeng/