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Re: parcellfun and rand

From: Jaroslav Hajek
Subject: Re: parcellfun and rand
Date: Wed, 8 Sep 2010 09:10:55 +0200

On Wed, Sep 8, 2010 at 9:07 AM, Jaroslav Hajek <address@hidden> wrote:
> On Tue, Sep 7, 2010 at 9:48 PM, Francesco Potortì <address@hidden> wrote:
>>>> For Monte Carlo simulations, note that they are not reproducible, as the
>>>> number of jobs scheduled to each process is not predictable.
>>>which gives you another interesting random number generator ;-)
>> Yes, with too little entropy to be useful, and too much for being
>> harmless :)
>>>I guess no way of making it reproducible?
>> As far as I understand (the implementation is Jaroslav's, I only made
>> some patches to the random number part) one would need to rewrite the
>> core implementation, which is based on a first-come first-served
>> criterion.  To gain reproducibility one would need to do a static
>> scheduling beforhand, and assign a given list of jobs to a given process
>> in a deterministic way.  I would definitely find a use for something
>> like that, as I use monte Carlo myself.  Moreover, that would be a
>> scheme simpler to implement with respect to the current one.
> Yes, it would be simpler (even way simpler) but unfortunately less
> efficient (sometimes much less). Dynamic scheduling accounts for
> unequal load of the slave processes, either because of unequal cost of
> jobs or because of OS's background work. With static scheduling,
> everything is left to the OS, which may do a poor job. Besides, if the
> cost of jobs varies, your a priori distribution of jobs may well
> happen to be the worst one :(
> If someone wants to make a static scheduling implementation, I'm not
> opposed to it, but I myself have no need for it. The current
> parcellfun code is already big enough so it should probably be an
> extra function and only be called from parcellfun as a special case.

Btw., OK to release the new changes in general 1.2.2?

RNDr. Jaroslav Hajek, PhD
computing expert & GNU Octave developer
Aeronautical Research and Test Institute (VZLU)
Prague, Czech Republic

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