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Re: Multiple independent random number streams cannot be implemented.
Posted:
Mar 15, 2013 1:46 AM


In article <khsbbv$36f$1@smc.vnet.net>, Roger Wilson <rogerhw999@gmail.com> 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.
SeedRandom[1] tells Mathematica to always start with a seed of 1.
The problem is that Random has internal state, so for independence you need multiple independent sets of internal state.
So f and g need to be in different BlockRandom domains.
Joe Gwinn



