
From:  David Bateman 
Subject:  Re: [OctDev] random numbers for distributed computations 
Date:  Mon, 11 Apr 2005 13:14:19 +0200 
Useragent:  Mozilla Thunderbird 0.8 (X11/20040923) 
Michael Creel wrote:
On Monday 11 April 2005 11:57, Francesco Potorti` wrote:I have a question about this. If a RNG has a period of X, that means that there are X unique values that are generated, and then the sequence repeats.No, it means that the sequence repeats after X values are produced. The period length says nothing about the space of values. However, for good general purpose generators, the size of the space of values is much smaller than the period.OK, you're saying that a generator with period 5 could produce values like 1 2 2 1 2 *** 1 2 2 1 2 *** 1 2 2 1 2 so the set of unique values is smaller than the period, correct?This may be, but for the moment my main question is whether the set of unique values that is generated depends upon the initial seed, or whether it's just the starting point in the sequence that depends on the initial seed. Could the unique values be 3 and 4, say, or will they always be 1 and 2?M.
The octaveforge generators are based on the Mersenne Twister, and it doesn't have a seed but rather a state of 32 values. So the unique starting points are defined from this state vector.. The period of the Mersenne Twister is 2^199371, so I wouldn''t worry about it repeating itself in yours or my lifetimes.
Regards David  David Bateman address@hiddenMotorola Labs  Paris +33 1 69 35 48 04 (Ph) Parc Les Algorithmes, Commune de St Aubin +33 1 69 35 77 01 (Fax) 91193 GifSurYvette FRANCE
The information contained in this communication has been classified as: [x] General Business Information [ ] Motorola Internal Use Only [ ] Motorola Confidential Proprietary
 Octave is freely available under the terms of the GNU GPL. Octave's home on the web: http://www.octave.org How to fund new projects: http://www.octave.org/funding.html Subscription information: http://www.octave.org/archive.html 
[Prev in Thread]  Current Thread  [Next in Thread] 