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Re: Gridding options [message #21558 is a reply to message #21497]

Wed, 30 August 2000 00:00

Craig Markwardt
Messages: 1869
Registered: November 1996

Senior Member

"J.D. Smith" <jdsmith@astro.cornell.edu> writes:

> Ben Tupper wrote:
>> (Sorry, JD, it does have loopity-loops. You can flick a worm into the
>> air... but that doesn't mean it knows how to fly! I'm still trying to
>> figure out what .....
>>
> ****************************************
> tt=total(a[(((dy=((di=lindgen(((n=nx<ny)),nx+ny-1)))/n))*(nx gt ny?1:nx)+ $
> (nx gt ny?1:-1)*((dx=di mod n))*(nx-1))>0<(nx*ny-1)]* $
> (dy ge dx AND (dy-dx) lt nx>ny),1)
> ****************************************
>>
>> means. Maybe I need to drink less/more coffee. )
>
> It's written in an ancient IDL runic language lost in the dark ages (1993).
> Simply run it on an array "a" after defining the dimensions "nx" and "ny" and
> all will be clear.

Another disadvantage to vectorizing with very large arrays is that IDL
has to generate the indices for the array dynamically. This can
consume a lot of memory (sometimes more than the array itself, if it's
a byte or int array!). The expression, lindgen((nx<ny), nx+ny-1),
[some deleted] is the giveaway that JD had to essentially create a
whole new array even bigger than the original. Still, it's a pretty
impressive computation.

Todd, did you compare the run time?

Craig

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

		Gridding options By: Ben Tupper on Tue, 29 August 2000 00:00
		Re: Gridding options By: Craig Markwardt on Wed, 30 August 2000 00:00
		Re: Gridding options By: davidf on Wed, 30 August 2000 00:00
		Re: Gridding options By: tclement on Wed, 30 August 2000 00:00
		Re: Gridding options By: Craig Markwardt on Wed, 30 August 2000 00:00
		Re: Gridding options By: John-David T. Smith on Wed, 30 August 2000 00:00
		Re: Gridding options By: Ben Tupper on Wed, 30 August 2000 00:00
		Re: Gridding options By: davidf on Thu, 31 August 2000 12:18
		Re: Gridding options By: tclement on Thu, 31 August 2000 12:08
		Re: Gridding options By: John-David T. Smith on Thu, 31 August 2000 11:33
		Re: Gridding options By: Craig Markwardt on Thu, 31 August 2000 08:56
		Re: Gridding options By: tclement on Thu, 31 August 2000 08:42

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