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Matrix multiplication problem fixed via dot operation.

• To: mathgroup at smc.vnet.net
• Subject: [mg64552] Matrix multiplication problem fixed via dot operation.
• From: Chris Young <c1572young at earthlink.net>
• Date: Wed, 22 Feb 2006 05:58:36 -0500 (EST)
• Sender: owner-wri-mathgroup at wolfram.com

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.

Chris Young

> In[3]:=
> \!\(\*
>   RowBox[{
>     RowBox[{"(", GridBox[{
>           {"a", "b"}
>           }], ")"}], ".",
>     RowBox[{"(", GridBox[{
>           {"c"},
>           {"d"}
>           }], ")"}]}]\)
> 
> Out[3]=
> {{a c+b d}}

• Follow-Ups:
  • Re: Matrix multiplication problem fixed via dot operation.
    • From: Andrzej Kozlowski <akoz@mimuw.edu.pl>
  • Re: Matrix multiplication problem fixed via dot operation.
    • From: Kristjan Kannike <kkannike@physic.ut.ee>