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Re: Assignment Time for a 3d Variable [message #46475 is a reply to message #46473]

Wed, 23 November 2005 07:57

David Fanning
Messages: 11724
Registered: August 2001

Senior Member

Nuno Oliveira writes:

> I was making a routine that was doing an intense assignment in one of
> the three directions possible, according to an option (either the first,
> second or third dimension). I noticed that when I was doing it in the
> first direction I took MUCH more time than in the other two directions.
>
> Anyone has a clue for why does this happen? And anyone knows a way that
> can make execution time similar? (Making the others to wait is not a
> valid answer, ;) )

The speed differences have to do with how you access different
parts of the array in memory. If the parts you want are contiguous,
then you can get them faster than you can if they are far apart in
memory. (Think how much faster it is to pick up the poker
chips when they are stacked than when they are scattered all
around the table.)

To make these kinds of assignments as fast as possible, use
the TRANSPOSE function to organize the data into the fastest
possible position:

IDL> Help, data
DATA BYTE = Array[3, 227, 149]
IDL> data = Transpose( Temporary(data), [2,3,1] )
IDL> Help, data
DATA BYTE = Array[227, 149, 3]

Cheers,

David

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

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[Message index]

		Re: Assignment Time for a 3d Variable By: Mark Hadfield on Wed, 23 November 2005 12:17
		Re: Assignment Time for a 3d Variable By: Foldy Lajos on Wed, 23 November 2005 11:13
		Re: Assignment Time for a 3d Variable By: David Fanning on Wed, 23 November 2005 11:09
		Re: Assignment Time for a 3d Variable By: James Kuyper on Wed, 23 November 2005 10:35
		Re: Assignment Time for a 3d Variable By: K. Bowman on Wed, 23 November 2005 10:16
		Re: Assignment Time for a 3d Variable By: Antonio Santiago on Wed, 23 November 2005 09:51
		Re: Assignment Time for a 3d Variable By: David Streutker on Wed, 23 November 2005 08:52
		Re: Assignment Time for a 3d Variable By: David Fanning on Wed, 23 November 2005 07:57
		Re: Assignment Time for a 3d Variable By: Antonio Santiago on Wed, 23 November 2005 04:46

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