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.