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Re: For loops vs. matrix operations [message #37433 is a reply to message #37427]

Wed, 17 December 2003 23:25

marc schellens[1]
Messages: 183
Registered: January 2000

Senior Member

Marshall Perrin wrote:
> Jonathan Greenberg <greenberg@ucdavis.edu> wrote:
>
>> 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
>>
>> ?
>
>
> Yes, the for loop version will be *vastly* slower. This is because IDL
> makes a seperate trip through the parse/interpret cycle for every pass
> through the for loop, greatly increasing the overhead.

Interpret cycle only. Parsing is only done once.

>> 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)...
>
>
> Matricize as much as you possibly can!

True always and anyway.

marc

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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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