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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: [mg64614] Re: Matrix multiplication problem fixed via dot operation.
  • From: Chris Young <c1572young at earthlink.net>
  • Date: Fri, 24 Feb 2006 00:18:09 -0500 (EST)
  • References: <dtjjgo$dfs$1@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

On 2006-02-23 01:08:24 -0500, Kristjan Kannike <kkannike at physic.ut.ee> said:

> Beware: though you got no error messages in case of multiplying square
> matrices with a space between them (as opposed to a dot), the result is
> NOT a dot product (matrix multiplication), but the matrices are multiplied
> element by element, e.g. if
> 
> C = A B
> 
> then
> 
> C[[1,1]] equals A[[1,1]] * B[[1,1]], etc. In short, the ordinary
> multiplication has the attribute Listable. (It can be very useful, e.g.
> when you have a vector variable x and a vector (list) of coefficients a,
> to compose them into a x.)

Thanks for the clarification.



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