Re: [OctDev] random numbers for distributed computations

[David B. <Dav...@mo...>]

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 octave-forge 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 2^19937-1, so I wouldn''t worry about it repeating 
itself in yours or my lifetimes.

Regards
David

-- 
David Bateman                                Dav...@mo...
Motorola Labs - Paris                        +33 1 69 35 48 04 (Ph) 
Parc Les Algorithmes, Commune de St Aubin    +33 1 69 35 77 01 (Fax) 
91193 Gif-Sur-Yvette FRANCE

The information contained in this communication has been classified as: 

[x] General Business Information 
[ ] Motorola Internal Use Only 
[ ] Motorola Confidential Proprietary