PoissonDistribution
- To: mathgroup at smc.vnet.net
- Subject: [mg16949] PoissonDistribution
- From: "Bernd Kaestner" <b.kaestner1 at physics.ox.ac.uk>
- Date: Thu, 8 Apr 1999 02:32:46 -0400
- Organization: Oxford University, England
- Sender: owner-wri-mathgroup at wolfram.com
Dear All,
I have a problem using the Statistics`DiscreteDistributions` package and was
wondering if anybody sees the same strange effekt, or even better, has a
solution to it.
The following command should produce a list of 10000 poisson distributed
numbers with mean <n>=100 :
<<Statistics`DiscreteDistributions`
poissonList=RandomArray[PoissonDistribution[100],10000];
For a poison distribution one should have <n>=<(n-<n>)^2> which also
Mathematica knows:
In[92]:=psList=PoissonDistribution[100]
Out[92]=PoissonDistribution[100]
In[93]:=Mean[psList]
Out[93]=100
In[94]:=Variance[psList]
Out[94]=100
However, when plotting the simulated values poissonList :
<<Statistics`DataManipulation`
freq=Frequencies[poissonList]
ListPlot[Table[{freq[[i,2]],freq[[i,1]]},{i,Length[freq]}],PlotRange->All]
Mathematica cuts off the lower half of the distribution, and produces
instead over 4000 (out of 10000) times the value 99.
Just in case it makes a difference: I have an IBM ThinkPad 1400, intel
pentium MMX 300MHz and tried it also on another pentium computer.
I would be glad some of you could try this as well, or provide a solution
for how to use this command.
Thank you in advance,
Bernd