RE: Random seed (RANDOMIZE)

From: Alfredo Ferrari <>
Date: Wed, 29 Jun 2011 16:47:16 +0200

... Chris proposal is naive and un-workable, and against what whichever
Monte Carlo does for godd reasons. Of course it would make it impossible
to have subsequent cycles following the same sequence, debugging the code
etc etc.

Reproducibility and predictability of the random number sequence implies
starting from a deterministically defined random seed. The code can in no
way know which sequences/up to which point have been already used in the
past for the same problem obviously.

I believe Denis question is different, if I understand correctly he would
like to have a way through a user routine to input something equivalent to
what is now input in what(2) of RANDOMIZe? Am I correct?


| Alfredo Ferrari || Tel.: + |
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On Tue, 28 Jun 2011, Alberto Fasso' wrote:

> Hi Chris,
> reproducing a random number sequence may not be important for the
> user, but is very important for whoever will have to debug a user
> input after a crash.
> The generator used in FLUKA is described in:
> G. Marsaglia and W.W Tsang
> The 64-bit universal RNG
> Statistics& Probability Letters 66, 183-187 (2004)
> I have not done myself tests as you suggest on that generator, but the authors
> and plenty of other people have. Look up "The 64-bit universal RNG" on
> Google and you will find many discussions about it.
> Alberto
> On Tue, 28 Jun 2011, Chris Theis wrote:
>> Alberto,
>>> You can input any number you want: how can it be more flexible???
>> from the user's point of view it would be more flexible if the user did not
>> have to input different seeds but the program makes sure by itself that
>> different runs are initiated with different values. The feature of
>> reproducability, which is without any question important for development and
>> sometimes also for a user, could be retained by specifically requesting it.
>> Most of the time the user is not interested in reproducing the random number
>> sequence and choosing a "good" seed is not necessarily trivial, depending on
>> the mathematical details of the RNG implementation. By the way, did you ever
>> investigate the influence of the chosen seeds on the cross-correlation and the
>> period of the implemented RNG? In case you do have test results or some
>> references for the one that is used I'd be interested and appreciate if you
>> would be willing to share them with me.
>> Cheers
>> Chris
>> -----Original Message-----
>> From: [] On Behalf Of Alberto Fasso'
>> Sent: 28 June 2011 16:03
>> To:
>> Cc: denis bertini
>> Subject: Re: Random seed (RANDOMIZE)
>> Denis,
>> can you please explain what do you mean by "not particularly flexible"?
>> You can input any number you want: how can it be more flexible???
>> What is your purpose in setting a seed from a user routine?
>> In any case any reference to function FLRNDM() changes the current random number. Is that what you want?
>> Alberto
>> On Tue, 28 Jun 2011, denis wrote:
>>> Dear Fluka experts,
>>> Could you tell me how to set a seed from a user fortran routine (
>>> putting a number with RANDOMIZE in the input file being not
>>> particularly flexible ) Thanks in advance,
>>> Denis Bertini
Received on Wed Jun 29 2011 - 17:21:01 CEST

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