From: Alberto Fasso' (Alberto.Fasso@cern.ch)
Date: Mon Jun 17 2002 - 17:11:17 CEST
The period of the FLRNDM random number generator is 2*144 = 10**43.
Now there is no need anymore to use "spaced" random seeds, because it is
possible to initiate up to 9.E8 independent sequences which will never overlap.
To this purpose, in the RANDOMIZE card set WHAT(2) = any number < 9.E8.
By default, this number is 54217137 (the number used as an example in the
G. Marsaglia and A. Zaman
A new class of random number generators
Ann. Appl. Probab. 1, 462-480 (1991)
but according to the authors, any number can be used (although I am
superstitious and prefer using some large odd number...)
On Fri, 14 Jun 2002 tap4@casino.PHYS.CWRU.Edu wrote:
> Hi Stefan,
> Laura and I have been using the FLRNDM random number generator
> together with the ranskip files that you sent, for our jobs on separate
> processors. We are having a problem with several jobs replicating the
> results of jobs started with earlier ranskip files. For instance, the
> job started with ranskip005 replicates the results from the latter
> part of the job started with ranskip004. Even if the random number
> ranges of the two jobs start to overlap, it is strange that they would
> be in phase. I don't think the random number generator has finished
> one or more cycles when this happens. I have an idea about why this is
> happening and am working to confirm it. However, I need some
> information about the random number generator and the the ranskip
> files. The questions I have are:
> 1. What is the period of the random number generator?
> 2. What is the spacing between the random seeds in the ranskip files?
> Please let me know if you have the answers.
> thank you,
-- Alberto FassÚ CERN-EP/AIP, CH-1211 Geneve 23 (Switzerland) Phone: (41 22) 767 2398 Fax: (41 22) 767 9480 Alberto.Fasso@cern.ch
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