[gate-users] uncorrelated random number seeds

[Dirk Kruecker]

> Dear Dirk,
>
> Thank you for your quick response.
>
> Although my generated seed files contain totally different numbers (only
> first line of all files is same as 9876), it is not guarantee for the

9876 identifys the stream. If you do a short simulation and save the random 
status afterwards you will be at a different position in the same stream, say 
a 1000 or so random numbers later. You may imagine the random number stream 
as a fixed list of random numbers. Starting at different positions will not 
give you independent numbers. On the other hand since each simulated event 
will consume a different amount of random numbers it is not so obvious that 
such a procedure creates corelated results. Anyhow with the random seeds 
files I  send you, you on the safe side each one starts an independent stream 
i.e. a different list of random numbers.

Hope it helps 
Dirk 

> independencies of these files, isn't it?
>
> I will try simulations with your seeds.
>
> regards,
>
> Hiroshi
>
>  From: Dirk Kruecker <d.kruecker at fz-juelich.de>
> Subject: Re: [gate-users] uncorrelated random number seeds
> Date: Mon, 17 Oct 2005 10:36:46 +0200
> Message-ID: <200510171036.46083.d.kruecker at fz-juelich.de>
>
> > Dear Hiroshi
> >
> > the method  Mutanga Theodore described does not create independent random
> > seeds but in most cases this should not be a real problem.  Maybe there
> > is some other reason for your results but it is difficult to say what the
> > reason is for the correlations you see. I posted a detailed explaination
> > how to handle the random files on this list at Jun 30, 2005. I also
> > include a set of random seed files that are indepent for sure.
> >
> > Best regards
> > Ditrk
> >
> > Am Montag, 17. Oktober 2005 09:01 schrieb Hiroshi Watabe:
> > > Dear Gate-users,
> > >
> > > I try to do 4 simulations with different seeds. In the past gate-users
> > > talk, I found the article (posted by Mutanga Theodore on 17 Dec 2004)
> > > which explain how to generate different seeds files.
> > > As the article explains, I did mock simulation with 10 Bq source and
> > > generated four different endOfRun.rndm. By using the command
> > > /random/resetEngineFrom, I initialized random seeds.
> > > I supposed to get four different results but four simulations produced
> > > very similar results. I say "similar" because I got exactly same
> > > projection data but the root outputs were slightly different in each
> > > others. In the root file, I found only event ID and time
> > > were different but else (for instance, source position and global
> > > position) were exactly same in Singles trees (I'm doing SPECT
> > > simulation).
> > >
> > > Any suggestions and advice are appreciate.
> > >
> > > Hiroshi
> > >
> > > --------------------------------------------------
> > >              Hiroshi Watabe, PhD
> > >
> > > watabe at ri.ncvc.go.jp
> > > Department of Investigative Radiology
> > > Advanced Medical Engineering Center
> > > National Cardiovascular Center Research Institute
> > >
> > > 5-7-1 Fujishirodai, Suita, Osaka 565-8565
> > >
> > > Tel:06-6833-5012-2560 or 06-6833-5004-2560
> > > Fax:06-6835-5429
> > > --------------------------------------------------
> > >
> > > _______________________________________________
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>
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