Re: Variation of results in iterations

From: Jérôme Hénin (
Date: Mon Dec 06 2004 - 19:01:32 CST


As far as I know, two runs using exactly the same simulation parameters and
starting point, run on the same machine, and without Langevin dynamics (or
specifying the seed for the pseudo-random generator), should behave exactly
the same way, because the machine itself is supposed to be deterministic.

If any of the above criteria is not met, the two simulations are likely to
differ very slightly after a few hundred steps, which is to say that they may
be wildly different after an average-sized run.

Does something in your experience go against this? If yes, I would be
interested to read more about it.


Le mardi 07 Décembre 2004 00:25, vous avez écrit :
> NAMD Friends,
> I have a question.
> When we run simulations(optimisation or MD) for any
> system under identical condition three times, we end up with results
> which are not exactly same but
> vary within a range, which we denote by error bar in the plot. My
> question is inspite of everything remaining same, what could be the
> possible reasons giving rise to
> these differences in results? Is it because of computation error ? or
> anywhere in calculation in NAMD any other parameters involved which
> causes so.
> Any suggestions and references highly appreciated.
> Pijush Ghosh.

Jérôme Hénin
Equipe de Dynamique des Assemblages Membranaires
Université Henri Poincaré / CNRS    UMR 7565
B.P. 239        54506 Vandoeuvre-lès-Nancy Cedex
Tel : (33) 3 83 68 43 95        Fax : (33) 3 83 68 43 71

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