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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 UTC4, Roger Wilson wrote: > Hopefully the title is enough of a red flag for someone to try to prove me wrong. > > > > I want to implement two functions; lets call them f and g so that they both return random numbers. For example... > > > > f[]:=RandomReal[]; > > g[]:=RandomReal[]; > > > > 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. > > > > In the above case (on my machine)... > > SeedRandom[1]; {f[], g[]} gives {0.168697, 0.113119} > > > > and of course.. > > SeedRandom[1]; {g[], f[]} gives the same {0.817389, 0.11142} > > > > Essentially I want f and g to to be independent random sources. > > > > 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. > > > > Roger



