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Re: vectorising versus loops [message #38144 is a reply to message #38135]

Sun, 22 February 2004 10:50

David Fanning
Messages: 11724
Registered: August 2001

Senior Member

Neil writes:

> Does anyone know what the speed increase factor is in IDL programmes
> when going from "do loops" to full vectorisation of arrays?

Would you believe a factor of 8100? Read it and weep:

http://www.dfanning.com/code_tips/slowloops.html

> I know all
> programmes are different and not every process lends itself to
> vectorisation. However, there must be some rule of thumb, ie speed
> going as a linear function of the number of array elements times some
> factor.

I think the generally accepted rule of thumb is that speed increases
exponentially with the number of JD Smith articles you have read.

> Also, are there any tricks to play if you want to vectorise loops that
> have IF statement decision in them, or any general rules for neat
> vectorisation of looped programmes?

Oh, lots and lots of articles. A google search on "FOR loops" AND
"slow" should turn up at least a week of good reading. :-)

Cheers,

David
--
David Fanning, Ph.D.
Fanning Software Consulting
Coyote's Guide to IDL Programming: http://www.dfanning.com/

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[Message index]

		Re: vectorising versus loops By: David Fanning on Mon, 23 February 2004 05:47
		Re: vectorising versus loops By: Edd Edmondson on Mon, 23 February 2004 01:41
		Re: vectorising versus loops By: David Fanning on Sun, 22 February 2004 10:50
		Re: vectorising versus loops By: Craig Markwardt on Sun, 22 February 2004 10:43
		Re: vectorising versus loops By: nasalmon on Mon, 23 February 2004 15:42
		Re: vectorising versus loops By: nasalmon on Sun, 07 March 2004 05:07

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