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Math Forum » Discussions » Software » comp.soft-sys.matlab

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

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Matt J

Posts: 4,976
Registered: 11/28/09
Re: matrix multiplication with zero dimensions
Posted: Jan 6, 2013 7:32 PM
  Click to see the message monospaced in plain text Plain Text   Click to reply to this topic Reply

"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.

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