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Matrix algebra and index order, A # B vs A ## B [message #79655]

Mon, 26 March 2012 04:33

Mats Löfdahl
Messages: 263
Registered: January 2012

Senior Member

IDL has two operators for matrix multiplication, # and ##. The former assumes the matrices involved have colum number as the first index and row number as the second, i.e., A_{rc} = A[c,r] with mathematics on the LHS and IDL on the RHS. The latter operator makes the opposite assumption, A_{rc} = A[r,c].

I believe much headache can be avoided if one chooses one notation and sticks with it. If it were only me, I'd choose the A_{rc} = A[r,c] notation. But it isn't only me, because I like to take advantage of IDL routines written by others. So, has there merged some kind of consensus among influential IDL programmers (those that write publicly available routines that are widely used - thank you BTW!) for which convention to use?

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[Message index]

		Matrix algebra and index order, A # B vs A ## B By: Mats Löfdahl on Mon, 26 March 2012 04:33
		Re: Matrix algebra and index order, A # B vs A ## B By: Mats Löfdahl on Wed, 28 March 2012 03:45
		Re: Matrix algebra and index order, A # B vs A ## B By: Mats Löfdahl on Thu, 05 April 2012 07:55
		Re: Matrix algebra and index order, A # B vs A ## B By: David Fanning on Tue, 27 March 2012 06:27
		Re: Matrix algebra and index order, A # B vs A ## B By: Craig Markwardt on Tue, 27 March 2012 06:11
		Re: Matrix algebra and index order, A # B vs A ## B By: Mats Löfdahl on Tue, 27 March 2012 00:45
		Re: Matrix algebra and index order, A # B vs A ## B By: Craig Markwardt on Mon, 26 March 2012 15:41
		Re: Matrix algebra and index order, A # B vs A ## B By: David Fanning on Mon, 26 March 2012 07:35
		Re: Matrix algebra and index order, A # B vs A ## B By: Mats Löfdahl on Thu, 05 April 2012 10:29
		Re: Matrix algebra and index order, A # B vs A ## B By: Kenneth P. Bowman on Thu, 05 April 2012 09:48
		Re: Matrix algebra and index order, A # B vs A ## B By: David Fanning on Thu, 05 April 2012 08:22

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