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From: njk@diku.dk (Niels J|rgen Kruse)
Newsgroups: comp.parallel
Subject: Re^2: Distributed simulation
Message-ID: <5347@hubcap.clemson.edu>
Date: 1 May 89 12:11:19 GMT
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matloff%mole.Berkeley.EDU@ucbvax.Berkeley.EDU (Norman Matloff) writes:

>Here is the setting.  It's discrete-event simulation, which many or most
>of your references are concerned with, on multiple-processor systems
>(tightly or loosely coupled).  Let P be the number of processors and T
>be the amount of run time needed to get the desired statistical accuracy.

>Moreover, it seems to me that the best method is also the simplest  --
>just have all P processors run the uniprocessor version of the program,
>but for T/P amount of run time, instead of T.  [Of course, each processor
>needs to use a different random number seed.]

Beware! It is not uncommon for pseudo random number generators
to show a much reduced independence between streams generated
from different seeds, compared to the independence within each
stream.

For instance, the Bsd random suffer from this. If you sample the
2 least significant bits, collect them to form 7 bit numbers
(discarding the least significant), take an equal number of
samples from more than 15 or so streams, perform chi square
analysis on the samples, you will get a value *well* above the
0.99 percentile.
-- 
         Niels J|rgen Kruse
Email    njk@diku.dk
Mail     Tustrupvej 7, 2 tv, 2720 Vanlose, Denmark