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Re: Is it really more efficient to work with arrays than FOR loops? [message #51513 is a reply to message #51493]

Thu, 23 November 2006 09:13

David Fanning
Messages: 11724
Registered: August 2001

Senior Member

Alvin writes:

> I was wondering if it is really that more efficient to work with arrays
> (large ones that is). For example I have the following simple code,
> which takes about 30 min to run:
>
> FOR z=0L, 400 DO BEGIN
> FOR y=0L, 400 DO BEGIN
> FOR x=0L, 400 DO BEGIN
> fn=f(z) ;a function of z
> gn=f(z) ;another function of z
> IF ( f(z) * x + g(z) * y GE f(z) * g(z) ) THEN BEGIN
> blah
> blah
> blah
> ENDIF
> ENDFOR
> ENDFOR
> ENDFOR
>
> Now if I tried to vectorize the above, would it do me any good in
> saving time and possibly memory? If I say something like f(z) # x +
> g(z) # y, where these are all vectors, I have a feeling that I am not
> covering all the possible combinations as the FOR loop above. Does
> anyone have any ideas, or suggestions?

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

Cheers,

David
--
David Fanning, Ph.D.
Fanning Software Consulting, Inc.
Coyote's Guide to IDL Programming: http://www.dfanning.com/
Sepore ma de ni thui. ("Perhaps thou speakest truth.")

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[Message index]

		Re: Is it really more efficient to work with arrays than FOR loops? By: Alvin on Fri, 24 November 2006 02:34
		Re: Is it really more efficient to work with arrays than FOR loops? By: David Fanning on Thu, 23 November 2006 09:13
		Re: Is it really more efficient to work with arrays than FOR loops? By: Jean H. on Thu, 23 November 2006 08:40
		Re: Is it really more efficient to work with arrays than FOR loops? By: Paolo Grigis on Thu, 23 November 2006 07:21

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