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Forum: Run Management
Re: Question Random generator correlation on quad-core PC (Ilya)
Date: 08 Jun, 2007
From: Vladimir IVANTCHENKO <vnivanch@mail.cern.ch>

On Fri, 8 Jun 2007, Ilya wrote:

> *** Discussion title: Run Management
> Email replies to PublicHyperNews@slac.stanford.edu must include:
>   In-Reply-To: <"/runmanage/189"@geant4-hn.slac.stanford.edu>
>   Subject: ...change this to be about your reply.
> 
> Dear all,
> 
> I have encountered a problem for which I don't see immediate solution. I
> am running 4 instances of one simulation program on a quad-core PC.
> These simulations use each different random seed numbers that are
> restored from different files in the beginning of run (similar as in
> /examples/novice/N03). I am using the defaul random generator.
> 
> Normally if I run the simulations on different PC's I get perfectly
> uncorrelated outputs. But after looking at the results obtained in 4
> simulations on quad-core PC I found that the outputs are almost
> identical (only few events out of 3e6 are different).
> 
> I start the simulations within about 1 min time interval.
> 
> Can somebody explain why this happens (I guess it is due to some
> correlation of random generators but why...?)? And how to avoid this
> correlation?
> 
> I am using GEANT4.8.2.p1 under SUSE Linux
> 
> Thanks a lot for help, Ilya.
> 

Hello,

If you use saving of random numbers per event and restore random numbers 
from file you share the same file for all processes. In that case you need 
run 4 applications from different subdirectories.

VI

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