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Re: For loops vs. matrix operations [message #37439 is a reply to message #37438]

Wed, 17 December 2003 14:57

Craig Markwardt
Messages: 1869
Registered: November 1996

Senior Member

"Jonathan Greenberg" <greenberg@ucdavis.edu> writes:

> I know some matrix programs perform better if you do straigh matrix math vs.
> a for-next loop -- is idl this way? E.g. is:
>
> array=intarr(10000)
> for i=0,(10000-1) do begin
> array[i]=array[i]+1
> endfor
>
> MUCH slower than:
>
> array=intarr(10000)
> array=array+1
>
> ?
>
> I'm trying to figure out how much time I should be using rewriting some code
> to optimize the algorithm, which is why I'm asking (the code is more complex
> than above, obviously, but I did notice I could "matricize" some of the code
> in places)...

The simplest answer is... optimize the slowest parts. To be a little
more specific, the slowest parts are usually the innermost loops,
which in your case above *is* the loop. If you can find obvious
things like the one you listed above, then definitely do it.

One nice feature of IDL which I didn't know about until recently is
PROFILER. While it doesn't give a line-by-line breakdown of execution
time, it does give a function-by-function one. If you have more than
a few routines, PROFILER should be able to tell you where to start
optimizing first.

Happy optimizing!
Craig

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Craig B. Markwardt, Ph.D. EMAIL: craigmnet@REMOVEcow.physics.wisc.edu
Astrophysics, IDL, Finance, Derivatives | Remove "net" for better response
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[Message index]

		Re: For loops vs. matrix operations By: David Fanning on Thu, 18 December 2003 04:55
		Re: For loops vs. matrix operations By: marc schellens[1] on Wed, 17 December 2003 23:25
		Re: For loops vs. matrix operations By: Kenneth P. Bowman on Wed, 17 December 2003 18:59
		Re: For loops vs. matrix operations By: JD Smith on Wed, 17 December 2003 17:31
		Re: For loops vs. matrix operations By: James Kuyper on Wed, 17 December 2003 15:52
		Re: For loops vs. matrix operations By: Wonko[3] on Wed, 17 December 2003 15:24
		Re: For loops vs. matrix operations By: Craig Markwardt on Wed, 17 December 2003 14:57
		Re: For loops vs. matrix operations By: mperrin+news on Wed, 17 December 2003 15:05

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