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Forum: Run Management
Re: Question random num generator initialization (Valery Taranenko)
Date: 03 Dec, 2009
From: Tom Roberts <Tom Roberts>

When submitting many parallel jobs, it is indeed essential to use different random number generator seeds. What I do is use the event number as the seed, at the beginning of each event. Then the problem reduces to making sure that each job uses different event numbers (e.g. via command-line arguments specifying first and last event numbers). This has several advantages:
* the seed is simply an integer
* you don't need to keep track of the seeds used
* usually you need to use different event numbers anyway
* no dependence on non-portable initializers (such as your problem)
* you can re-run the entire job
* you can re-run INDIVIDUAL EVENTS

This last is the most important reason to do this: often when you run thousands or millions of events you get a few "outlier" events that are far outside the normal distribution of some histogram. All you need to do is determine their event numbers, and you can re-run them with visualization enabled and SEE what happened. I have a feature in the histogramming tool I use that makes this easy.

The default Geant4 pseudo random number generator (from CLHEP) guarantees independent streams for seeds in the range 0 to 900,000,000 -- that's more than enough events for my purposes.

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1 Agree: Re: random num generator initialization   (Valery Taranenko - 03 Dec, 2009)
(_ None: Re: random num generator initialization   (Tom Roberts - 03 Dec, 2009)
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