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MathGroup Archive 2004

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Re: Matrix Dot Product

  • To: mathgroup at smc.vnet.net
  • Subject: [mg52182] Re: [mg52159] Matrix Dot Product
  • From: Hugh Walker <hwalker at gvtc.com>
  • Date: Sun, 14 Nov 2004 04:30:20 -0500 (EST)
  • Sender: owner-wri-mathgroup at wolfram.com

On Saturday, November 13, 2004, at 03:40 AM, MacDonald, Calum ((MAT)) 
wrote:

> Hi
>
> I was wondering if someone could please help me with a command for
> calculating the dot product of two (NxN) matrices.
>
> For example, for  two (2x2) matrices, A and B, we define the dot 
> product
> as:
>
> A(1,1)*B(1,1) + A(2,1)*B(2,1) + A(1,2)*B(1,2) + A(2,2)*B(2,2)
>
> i.e. we multiply corresponding entries of the matrices and sum these
> values.
>
> It is easy to write this in a loop but for large matrices the
> calculation is rather slow.
>
> Is there a Mathematica function that I can call that will allow me to 
> do
> this faster?
>
> Thanks
>
> Calum


Let aMat and bMat each be nXn matrices. One way to compute your "dot 
prod', surely faster than looping, is

(a//Flatten).(b//Flatten)

==========
Hugh Walker
Gnarly Oaks


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