[R] Strange means of numbers drawn from rpois
Alan Arnholt
arnholt at math.appstate.edu
Wed Nov 8 15:55:23 CET 2000
Kjetil,
I get "expected" results using a windows machine version
1.1.1.
> sapply(1:15, function(n) mean(rpois(1000000, n)))
[1] 1.000284 1.999766 3.001319 4.000618 5.000408 6.003184 7.000026 7.997165 9.000461 9.514773 11.000396
[12] 12.128740 13.160210 14.177194 15.193355
> sapply(1:15, function(n) mean(rpois(1000000, n)))
[1] 1.000726 2.000776 3.000708 4.000043 5.001959 6.001235 7.002085 7.998147 9.000528 9.901534 10.999140
[12] 12.124794 13.152148 14.182332 15.007930
> sapply(1:15, function(n) mean(rpois(1000000, n)))
[1] 1.000320 2.001331 3.002032 4.004577 4.999679 6.000778 6.997700 8.002213 9.005890 9.764240 10.786886
[12] 11.822689 12.863624 13.904637 15.000833
> sapply(1:15, function(n) mean(rpois(100000, n)))
[1] 1.00049 1.99307 2.99624 3.99277 5.00063
[6] 6.00018 6.99672 8.01585 8.98921 9.76499
[11] 10.76767 11.78713 12.82248 13.85002 14.89385
> sapply(1:15, function(n) mean(rpois(100000, n)))
[1] 0.99788 2.00799 3.00712 3.98751 4.99152
[6] 5.99747 7.01120 7.99749 9.00031 9.73359
[11] 10.75011 12.00378 13.11141 14.14407 15.17481
> sapply(1:15, function(n) mean(rpois(100000, n)))
[1] 1.00198 1.98872 3.00582 3.99331 4.99453
[6] 6.01429 6.99885 7.98966 8.99976 9.87061
[11] 10.90451 11.99415 13.13388 14.15692 15.16398
> sapply(1:15, function(n) mean(rpois(100000, n)))
[1] 0.99634 1.99840 3.00492 3.99907 4.99878
[6] 6.00134 7.00225 7.98363 8.99210 9.85822
[11] 10.89415 12.00827 13.12437 14.16350 14.99912
On Wed, 8 Nov 2000 15:09:24 +0100 (MET) Kjetil Kjernsmo
<kjetil.kjernsmo at astro.uio.no> wrote:
> Dear all,
>
> I think I must be going crazy.... If I do
> > mean(rpois(1000000, 14))
> I get:
> [1] 13.50420
> and again:
> > mean(rpois(1000000, 14))
> [1] 13.49896
> > mean(rpois(1000000, 14))
> [1] 13.50161
> > mean(rpois(1000000, 15))
> [1] 14.49250
> > mean(rpois(1000000, 15))
> [1] 14.49897
> > mean(rpois(1000000, 14.5))
> [1] 13.99689
> > mean(rpois(1000000, 14.5))
> [1] 13.9963
>
> This was on a
> platform alphaev6-dec-osf4.0e
> major 1
> minor 1.1
> checking out on a
> platform sparc-sun-solaris2.7
> major 1
> minor 1.0
> I get the same
> > mean(rpois(100000, 14.5))
> [1] 14.00347
> > mean(rpois(100000, 14.5))
> [1] 14.00667
> > mean(rpois(100000, 14.5))
> [1] 14.00675
>
> It's fishy, isn't it...? I have generated lots of numbers, but I haven't
> seen anything like this before....
>
> I have also done
>
> > sapply(1:15, function(n) mean(rpois(1000000, n)))
> [1] 1.000052 1.999150 2.996975 4.003843 4.996136 5.999065 6.999725
> [8] 7.998869 9.003127 9.518397 10.512347 11.500405 12.510494 13.499788
> [15] 14.504661
>
> So, something happens at 10... And again:
>
> > sapply(1:15, function(n) mean(rpois(1000000, n)))
> [1] 1.000173 2.001639 2.997016 4.000163 5.000802 5.992751 6.999794
> [8] 7.997315 8.998479 9.517824 10.508328 11.507336 12.501885 13.502146
> [15] 14.496810
>
> Starting with --vanilla gives pretty much the same result...
>
> trying different RNGs:
> > RNGkind("Mersenne")
> > sapply(1:15, function(n) mean(rpois(1000000, n)))
> [1] 1.000563 1.998802 2.998526 3.997537 4.999230 5.996591 6.999596
> [8] 7.998982 9.000783 9.510220 10.509562 11.505009 12.505001 13.504522
> [15] 14.500956
> > RNGkind("Knut")
> > sapply(1:15, function(n) mean(rpois(1000000, n)))
> [1] 0.999031 2.000444 3.002296 3.997795 4.998880 5.995267 7.001894
> [8] 7.999983 9.000267 9.513537 10.507142 11.502634 12.498944 13.498615
> [15] 14.502410
>
> After printing rpois (to see that I haven't replaced it with something
> strange) and version, I call
> > plot(sapply(1:15, function(n) mean(rpois(1000000, n))), t='l')
> getting a plot that isn't a straight line, and then:
> > sapply(1:15, function(n) mean(rpois(1000000, n)))
> [1] 0.997961 1.999509 3.000748 3.999825 5.002983 6.004424 6.998825
> [8] 7.997999 8.998341 9.766942 10.781751 11.817181 12.856154 13.900369
> [15] 14.999378
> and again:
> > sapply(1:15, function(n) mean(rpois(1000000, n)))
> [1] 0.998570 2.000155 2.999534 4.002987 4.997999 5.996326 6.996761
> [8] 7.996728 8.997265 9.764972 10.793913 11.822874 12.859886 13.903846
> [15] 15.000311
>
> Weird....?
>
> Best,
>
> Kjetil
> --
> Kjetil Kjernsmo
> Graduate astronomy-student Problems worthy of attack
> University of Oslo, Norway Prove their worth by hitting back
> E-mail: kjetikj at astro.uio.no - Piet Hein
> Homepage <URL:http://www.astro.uio.no/~kjetikj/>
> Webmaster at skepsis.no
>
>
> -.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-
> 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 at stat.math.ethz.ch
> _._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._
----------------------
Alan T. Arnholt
Associate Professor
Dept. of Mathematical Sciences
TEL: (828) 262-2863
FAX: (828) 265-8617
arnholt at math.appstate.edu
-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-
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 at stat.math.ethz.ch
_._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._
More information about the R-help
mailing list