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Topic: matrix multiplication with zero dimensions
Replies: 11   Last Post: Jan 7, 2013 10:20 AM

 Messages: [ Previous | Next ]
 Matt J Posts: 4,997 Registered: 11/28/09
Re: matrix multiplication with zero dimensions
Posted: Jan 6, 2013 7:32 PM

"Bruno Luong" <b.luong@fogale.findmycountry> wrote in message <kcd1lg\$6u4\$1@newscl01ah.mathworks.com>...
> "Matt J" wrote in message <kcd0g0\$34t\$1@newscl01ah.mathworks.com>...
>
>
> Just like sum([]), prod([]), this result is no exception so to be documented separately.

==============

I can see the rational behind sum([])=0and prod([])=1. It's so that

sum([A,[]],2)=sum(A,2)+sum([])
prod([A,[]],2)=prod(A,2)*prod([])

I do not see the rationale behind the originally posted relationship, though. Taking a slightly different example, I can see perhaps that

ones(3,0)*ones(0,3)

should end up being 3x3 because of the outer dimensions, but why should it end up containing zeros.

Date Subject Author
1/6/13 Matt J
1/6/13 Bruno Luong
1/6/13 Matt J
1/6/13 Roger Stafford
1/6/13 Matt J
1/7/13 Matt J
1/7/13 Roger Stafford
1/7/13 James Tursa
1/7/13 Roger Stafford
1/7/13 Matt J
1/7/13 Bruno Luong
1/7/13 Steven Lord