RE: parallel mode

From: Chris Theis (
Date: Mon Oct 22 2007 - 19:02:35 CEST

  • Next message: Joel DeWitt: "Particle LET"

    Hello Konstantin,

    to my knowledge there is no "built-in" way to automatically generate a
    number of parallel inputs. Thus, I assume you will have to resort to a
    script to generate a number of RANDOMIZ cards.

    > I wonder if there is a more convenient way do set the random number
    > generator seed for parallel mode tasks. For instance, one could set
    > WHAT(2) to some specific value in order to initialize the seed to the
    > current machine clock and use the same input file for all parallel
    > jobs.

    Even though the idea of initializing the seed to the current machine
    clock is tempting at first sight there are a couple of quite subtle
    issues that arise. First of all by doing this you will lose the
    possibility to easily reproduce the exact sequence of random numbers
    that will be used throughout your simulation. Especially for debugging
    purposes this feature is quite important and should not be disregarded
    so quickly.=20

    Second, all statistics that you will most likely do with the results of
    your individual runs, are based on the (more or less valid) assumption
    that the respective random observables are independently distributed.
    Using the machine clock for seeding it is possible to introduce subtle
    cross-correlations in the sequence of random numbers which render your
    "common" formulas for variance etc. invalid. Furthermore, using
    disadvantageous seeds can influence the period of your random number
    generator. However, the impact of points two and three are highly
    implementation dependent and one would have to do a whole bunch of
    statistical tests (auto- & cross correlation, calculation of the
    statistical momenta including the covariance matrix, etc. etc.) to check
    the actual impact. I guess this is something one usually wants to stay
    away from as it's neither trivial nor much fun to do.

    Therefore, I'd very much discourage to use the clock as a seed
    generation mechanism.=20

    Best regards

  • Next message: Joel DeWitt: "Particle LET"

    This archive was generated by hypermail 2.1.6 : Mon Oct 22 2007 - 21:04:07 CEST