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Topic: Multiple independent random number streams cannot be implemented.
Replies: 3   Last Post: Mar 16, 2013 3:13 AM

 Messages: [ Previous | Next ]
 Vince Virgilio Posts: 135 Registered: 4/30/05
Re: Multiple independent random number streams cannot be implemented.
Posted: Mar 15, 2013 1:46 AM

It is possible, but I found it requires a couple of layers of abstraction.
(Perhaps there's an easier way.)

Basically, wrap calls to RandomReal[] etc. with something that can hold persistent state. On each call, SeedRandom[lastState], then lastState = Random`GetRandomState[]. The body looks something like this:

method[Hold[e__] ] := BlockRandom[SeedRandom@lastState;
With[{result = e}, lastState = Random`GetRandomState[]; result]];

(Implementation of <object>`method not shown. It uses my own flyweight OO framework.)

This has allowed me to run an arbitrary number of unique and reproducible random # streams.

Sorry that there's no time for more detail now.

Vince

On Thursday, March 14, 2013 7:13:03 AM UTC-4, Roger Wilson wrote:
> Hopefully the title is enough of a red flag for someone to try to prove me wrong.
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>
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> I want to implement two functions; lets call them f and g so that they both return random numbers. For example...
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> f[]:=RandomReal[];
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> g[]:=RandomReal[];
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> However I want f and g to return the same number when they're called for the nth time. So the first call to f is always the same number and the first call to g is always the same number.
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> In the above case (on my machine)...
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> SeedRandom[1]; {f[], g[]} gives {0.168697, 0.113119}
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> and of course..
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> SeedRandom[1]; {g[], f[]} gives the same {0.817389, 0.11142}
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> Essentially I want f and g to to be independent random sources.
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> It is possible to localize the random number generators using BlockRandom but I do not see how that helps me in this case. BlockRandom localizes the state of the random number generators within the block where as I want to localize them into the symbol names.
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> Roger

Date Subject Author
3/14/13 Roger Wilson
3/15/13 Vince Virgilio
3/15/13 Joseph Gwinn
3/16/13 Roger Wilson