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Message from discussion Global array operations: a performance hit?
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Dennis Wassel  
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 More options Jun 18 2008, 5:41 am
Newsgroups: comp.lang.fortran
From: Dennis Wassel <dennis.was...@googlemail.com>
Date: Wed, 18 Jun 2008 02:41:55 -0700 (PDT)
Local: Wed, Jun 18 2008 5:41 am
Subject: Re: Global array operations: a performance hit?
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On 18 Jun., 10:20, deltaquattro <deltaquat...@gmail.com> wrote:

> > 3) How did you measure execution time?
> > I find that accuarate timing on a computer is a nontrivial task. The
> > 'time' command on my machine shows up to 200% variance. I can only
> > assume you used some clever and appropriately precise way of
> > measuring.

> When Richard told you exactly the same, you didn't ask which "clever
> and appropriately precise way of measuring" he used, but you quickly
> thanked him for "enlightening us". I can only assume that for you
> using "some clever and appropriate precise way of measuring" means
> asking for Richard's agreement on the subject.

Hey, easy on the noobs!
That's outright flaming, when all I was trying to do is to help!
Had you earlier made any suggestion that you know yourself around
Fortran coding very well, thank you, I might as well have left
answering to the experts.
Instead you *now* post something I can summarise as "STFU n00b", which
tends to scare away new members. Not gonna cow me down, but others
would have left for good by now.

But then again, who am I telling? Of course you know all that!

> > I'm not a compiler specialist but AFAIK, array operations should not
> > usually be slower than explicit loop constructs.

> Well, then you could just try some example for yourself and see what
> happens. My experience comes from different CFD codes I wrote using
> whole array operations and single DO loops, and with my compiler I
> often found significant execution time differences in real life codes
> on real life cases.

That would have been insightful.

> Best regards,

> deltaquattro


 
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