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Re: vectorising versus loops [message #38135 is a reply to message #38129]

Mon, 23 February 2004 01:41

Edd Edmondson
Messages: 50
Registered: January 2003

Member

David Fanning <david@dfanning.com> wrote:
> 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

Funny, that. "I'm just an average astrophysicist" too, and last week I
took my IDL program that took a *fortnight* to run and got it down to 21
seconds. That's a speed up of 55,000 times and there wasn't even a nested
loop - just one loop with a bunch of IFs in it. Through use of plenty of
WHEREs (dealing with each case previously handled with an IF) and a REFORM
plus a HISTOGRAM it's stupidly faster.

In fact it's probably more than 55,000 times because a fair few seconds of
that is needed just to read in the data file at the start.

--
Edd

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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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