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MathGroup Archive 2006

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Re: Matrix multiplication problem fixed via dot operation.

  • To: mathgroup at smc.vnet.net
  • Subject: [mg64600] Re: Matrix multiplication problem fixed via dot operation.
  • From: Bill Rowe <readnewsciv at earthlink.net>
  • Date: Thu, 23 Feb 2006 00:35:37 -0500 (EST)
  • Sender: owner-wri-mathgroup at wolfram.com

On 2/22/06 at 5:58 AM, c1572young at earthlink.net (Chris Young) wrote:

>To answer my own posting, it looks like the "dot" operator is
>needed when the matrices aren't both square.

>E.g.: a row vector with components a and b times a column vector
>with components c and d will yield the correct result, the
>dot-product.

>I'm still puzzled why Mathematica doesn't do the same thing without
>the dot.

Because it is very useful to do things like:

In[3]:={a,b} {c,d}
Out[3]={a c,b d}

And since for me (and I suspect most others) the need to multiply lists of things in the manner above arises much more frequently than the need for matrix multiplication, I am glad Mathematica reserves the implied multiplication syntax for this rather than matrix multiplication when matrices are involved.
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