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# st: RE: RE: RE: RE: RE: RE: Stata stuck in loop with -rndpoi-?

 From "Nick Cox" To Subject st: RE: RE: RE: RE: RE: RE: Stata stuck in loop with -rndpoi-? Date Thu, 13 May 2010 16:32:19 +0100

```As someone said, if all else fails, look at the code. -viewsource
rndpoi- gets you there in one.

Nick
n.j.cox@durham.ac.uk

Karen Wright

Thank you very much for the help.
Karen

>>> "Martin Weiss" <martin.weiss1@gmx.de> 13/05/2010 16:06 >>>
<>

" You need something with a better algorithm."

-genpoisson-, as in -findit genpoisson, does not complain or behave
weirdly:

*************
clear*
set obs 10000
genpoisson x, mu(710)
su
hist x
*************

HTH
Martin

-----Original Message-----
From: owner-statalist@hsphsun2.harvard.edu
[mailto:owner-statalist@hsphsun2.harvard.edu] On Behalf Of Nick Cox
Sent: Donnerstag, 13. Mai 2010 16:57
To: statalist@hsphsun2.harvard.edu
Subject: st: RE: RE: RE: RE: Stata stuck in loop with -rndpoi-?

It's an underflow problem. -rndpoi- at one point calculates exp(-mean),
but try

. di exp(-710)

and you will get 0. Even if you get results for means near 700, they
will be of dubious accuracy. You need something with a better algorithm.
Alternatively, won't a Poisson with mean 700 look pretty near Gaussian
any way? I get the skewness and kurtosis to be

. di 1/sqrt(700)
.03779645

. di 3 + 1/700
3.0014286

which would cause broad and continuing smiles of pleasure in many
branches of statistical science.

Nick
n.j.cox@durham.ac.uk

Nick Cox

What I said in 2003 still holds.

Nick
n.j.cox@durham.ac.uk

Martin Weiss

http://www.stata.com/statalist/archive/2003-08/msg00197.html, though
things
may have changed materially in the meantime...

Karen Wright

Unfortunately my IT department has a problem with letting us upgrade
Stata,
they have to perform it and do not want to - which is why I was trying
to do
it without the ugrade.  Thank you, I shall just have to pester them
again!

>>> "Martin Weiss" <martin.weiss1@gmx.de> 13/05/2010 14:59:48 >>>

function...

Karen Wright

I am attempting to generate 10000 random number based on a poisson
distribution with mean from my data, using -rndpoi- (from ssc).
I seem to encounter a problem when the mean is greater than 700.  Would
anyone be able to help me, either with an alternative method of
producing
the figures I need, or what I am currently doing wrong?

************************

*this works:
rndpoi 10000 694.5
*this doesn't:
rndpoi 10000 710

************************
I am currently using Stata 10.0 on Windows.

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```