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MathGroup Archive 1995

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Re: Q: Random[]

  • To: mathgroup at christensen.cybernetics.net
  • Subject: [mg1634] Re: [mg1598] Q: Random[]
  • From: John Fultz <jfultz>
  • Date: Sat, 8 Jul 1995 02:35:25 -0400

> I am constructing a Monte-Carlo simulator in Mathematica for an 
> x-ray polarimeter we are proposing for NASA's Explorer program.  I 
> have 2 questions about Random[]:
> 
> 1.  What is its period?  This affects how large a Monte-Carlo I 
> can run before losing independence of trials.
> 
> 2.  I understand it gets its seed from the clock.  When debugging 
> Monte-Carlo code, I like to set the seed so I can repeat runs.  Is 
> this possible for Random[], and if so how?  (The seed initiates the 
> sequence of psuedo-random numbers.)
> 
> Ron Elsner                                  205-544-7741
> ES84                                        205-544-7754 (fax)
> NASA MSFC                                   elsner at avalon.msfc.nasa.gov
> Huntsville, AL 35812

Its period is somewhat above 10^400, so you shouldn't have to worry about
it cycling anytime in our lifetimes.

You might want to look in the "Major New Features in Mathematica
Version 2.2" pamphlet (pages 16-7) which shipped with Mathematica 2.2
(and in the case of the Windows version is also on-line).  Some new
features with the random number generator are discussed there.
Specifically, there's a new function called SeedRandom[].  Just
type:

	SeedRandom[n]

where n is any integer.  You can, of course, use this function to reseed
the random number generator for a predictable set of "random" numbers.

John Fultz
Wolfram Research, Inc.


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