<dolive <at> math.siu.edu> writes:
>
>
> 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.
>
Certainly fixed by 2.3.1:
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] 10.064 10.084 10.338 9.848 9.740 10.052 9.954 9.960 10.080 10.062
[11] 9.702 9.936 9.808 10.100 9.982 9.954 9.854 10.226 9.872 10.280
[21] 10.236 10.116 9.992 9.904 10.116 10.168 10.144 10.018 9.982 10.016
[31] 10.148 10.128 10.234 10.030 9.882 9.922 10.150 10.062 10.152 9.804
[41] 10.178 10.106 10.092 10.080 10.112 10.012 10.074 10.276 10.086 10.048
[51] 10.072 10.086 10.204 9.974 10.020 10.104 9.792 10.154 10.042 10.046
[61] 9.882 10.014 9.654 10.126 10.068 10.040 10.094 10.250 9.854 9.966
[71] 9.852 9.974 9.732 9.986 9.912 10.048 9.750 10.068 10.024 9.842
[81] 9.640 10.114 10.238 10.138 9.876 9.750 10.310 10.026 10.024 10.132
[91] 10.088 9.970 10.044 9.912 9.850 10.022 9.970 10.052 9.938 9.994
it's surprising that such a large bug would have persisted
even up to version 1.1.1. You should certainly upgrade your version,
but in the meantime you might try starting R in "vanilla" mode to
make sure you don't have a wonky local version of rpois or something
else lying around ...
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