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Re: IDL2MATLAB [message #29538 is a reply to message #29482]

Wed, 27 February 2002 14:43

Liam E. Gumley
Messages: 378
Registered: January 2000

Senior Member

Nigel Wade wrote:
> Liam E. Gumley wrote:
>
>> Ethan wrote:
>>>
>>
>>
>> A complicating factor is that in IDL, arrays are stored in column-major
>> order (the same as FORTRAN), while in Matlab, arrays are stored in
>> row-major order (the same as C).
>
> Substitute IDL for MATLAB. In IDL they are the same as in C. I can never
> remember which is column-major or row-major, but I know that using MATLAB
> multi-dimension matrices in C mex files is a real pain because of the array
> indexing difference.

I'll stick by my original comments, which referred to *arrays* only (not
matrices). In IDL and FORTRAN, an array with dimensions [m cols, n rows]
is stored contiguously in memory as

(col 1, row 1), (col 2, row 1), (col 3, row 1), ... (col m, row 1),
(col 1, row 2), (col 2, row 2), (col 3, row 2), ... (col m, row 2),
(col 1, row 3), (col 2, row 3), (col 3, row 3), ... (col m, row 3),
.
.
.
(col 1, row n), (col 2, row n), (col 3, row n), ... (col m, row n)

The term "column-major" is used because the column index varies the
fastest when accessing contiguous elements of a multi-dimensional array
in memory.

Cheers,
Liam.
Practical IDL Programming
http://www.gumley.com/

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[Message index]

		IDL2MATLAB By: the_cacc on Tue, 26 February 2002 05:02
		Re: IDL2MATLAB By: Mark Hadfield on Wed, 27 February 2002 16:35
		Re: IDL2MATLAB By: James Kuyper on Thu, 28 February 2002 08:00
		Re: IDL2MATLAB By: David Fanning on Wed, 27 February 2002 15:05
		Re: IDL2MATLAB By: Liam E. Gumley on Wed, 27 February 2002 14:43
		Re: IDL2MATLAB By: David Fanning on Wed, 27 February 2002 07:22
		Re: IDL2MATLAB By: thompson on Wed, 27 February 2002 07:09
		Re: IDL2MATLAB By: Martin Downing on Tue, 05 March 2002 07:23
		Re: IDL2MATLAB By: gutmann on Thu, 28 February 2002 15:07
		Re: IDL2MATLAB By: David Fanning on Thu, 28 February 2002 08:16

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