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Re: () and execution speed [message #44951 is a reply to message #44950]

Fri, 29 July 2005 09:41

David Fanning
Messages: 11724
Registered: August 2001

Senior Member

"Gert" <Gert.VandeWouwerNO @ SPAM.com> writes:

> I just played with and array of structures, each structure containing a
> (float) images.
> If i do
>
> SomeProc, psData[NumStruct].flIm[1:1000]
>
> or
>
> SomeProc, (psData[NumStruct].flIm)[1:1000]
>
> then the result is the same, but the second runs much slower. Anyone knows
> why this is so? My guess is that in the second run, a copy of the array is
> made.

Yes, the parentheses are creating a temporary copy to be
subscripted, I think.

> I would be interested to find out if there are more 'pitfalls' out there.

Oh, goodness. Then I would make a daily practice out of
consulting this newsgroup. You will be surprised what you
learn. :-)

Here are some examples:

http://www.dfanning.com/code_tips/asterisk.html
http://www.dfanning.com/code_tips/slowloops.html
http://www.dfanning.com/tips/forloops.html
http://www.dfanning.com/tips/forloops2
http://www.dfanning.com/ographics_tips/slowrendering.html

Cheers,

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

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		Re: () and execution speed By: Ken Mankoff on Fri, 29 July 2005 09:27
		Re: () and execution speed By: David Fanning on Fri, 29 July 2005 09:41

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