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Question Basic Question about Random Seeds 

Forum: Run Management
Date: 28 Aug, 2013
From: Martin Koslowsky <Martin Koslowsky>

This may seem like an incredibly stupid question, but it is also one that I have had difficulty finding an answer to, so please indulge me.

What exactly is a Seed? I believe I know what a Seed is in general, what I am unsure of is how it plays out in the context of the CLHEP classes.

Take, for example, the RanecuEngine class. It contains two methods that appear to be for setting seeds (SetSeed and SetSeeds). The description on the CERN website of the class is generally unhelpful - for example, I have no idea what the difference is between a "local" and "static" table of seeds. I therefore have little idea what the practical difference is between these two methods.

I also don't know what the two numbers that one inputs into SetSeeds are doing. My suspicion from looking at someone else's code is as follows: The first number (i.e. const long* seeds) is a way of selecting a parameter in the algorithm for generating pseudo-random numbers, which would allow me to generate separate lists of numbers that are independent of each other. Hence I would be able to add Monte Carlo results from a run which set seeds=1 with a run which set seeds=2 without committing a grave error. The second number (HepInt index) is, according to this hypothesis, basically for selecting where in the sequence of generated pseudo-random numbers one would like to start. However, I don't know for sure and that bothers me.

I am also interested in knowing how many numbers you can generate from a seed before you run into trouble.

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1 More: Re: Basic Question about Random Seeds   (Gabriele Cosmo - 03 Sep, 2013)
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