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Re: Dot Product of Vectors

  • To: mathgroup at smc.vnet.net
  • Subject: [mg9] Re: Dot Product of Vectors
  • From: Bill Rowe <readnews at sbcglobal.net>
  • Date: Sun, 25 May 2008 02:06:47 -0400 (EDT)

On 5/24/08 at 3:55 AM, gregory.lypny at videotron.ca (Gregory Lypny)
wrote:

>I've got two n x k matrices called X and Y.  I'd like to compute an
>n x 1 vector whose elements are the dot products of corresponding
>rows of X and Y, that is,

>{{X[[1]].Y[[1]]}, {X[[2]].Y[[2]]}, {X[[3]].Y[[3]]}, ...
>{X[[n]].Y[[n]]}.

>I found that this can be done using MapThread as

>MapThread[Dot, { X, Y}],

>which is straightforward.  I'm curious, given that there a zillion
>ways to do any given calculation in Mathematica, if anyone knows of
>another way that is as compact.

Another simple way to get the same result would be:

Total@Transpose[x y]


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