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Re: really stupid matrix question [message #94834 is a reply to message #94830]

Mon, 30 October 2017 12:46

wlandsman
Messages: 743
Registered: June 2000

Senior Member

I have always has trouble remembering column-major and row-major (and thus never use the terms) so I hope I don't confuse things here. But from Wikipedia

https://en.wikipedia.org/wiki/Row-_and_column-major_order

"A general way to order objects with many attributes is to first group and order them by one attribute, and then, within each such group, group and order them by another attribute, etc. If more than one attribute participate in ordering, the *first* would be called major and the last minor."

In column major, you first order by column, and then say within column zero you order by rows. So in column major, the *rows* are contiguous in memory.

-Wayne

On Monday, October 30, 2017 at 1:49:27 PM UTC-4, Ann Nonymous wrote:
> OK, before my head explodes, can anyone tell me the answer to this?
>
> a=indgen(4,3)
> print, a
> 0,1,2,3
> 4,5,6,7
> 8,9,10,11
>
> OK, are the horizontal lines really vertical vectors? I think they would be based on idl being column-major, which means the columns are contiguous in memory. If. I. understand. correctly.
>
> If this is correct, then why does IDL print them out in rows????
>
> Someone please shoot me.

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[Message index]

		really stupid matrix question By: astroboy.20000 on Mon, 30 October 2017 10:49
		Re: really stupid matrix question By: wlandsman on Mon, 30 October 2017 12:46
		Re: really stupid matrix question By: Burch on Mon, 30 October 2017 13:15
		Re: really stupid matrix question By: astroboy.20000 on Tue, 31 October 2017 10:45
		Re: really stupid matrix question By: astroboy.20000 on Tue, 31 October 2017 10:46
		Re: really stupid matrix question By: benjamin.castellani on Tue, 31 October 2017 12:51
		Re: really stupid matrix question By: astroboy.20000 on Wed, 01 November 2017 15:32

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