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Re: Dot Product of Vectors
*To*: mathgroup at smc.vnet.net
*Subject*: [mg20] Re: [mg89044] Dot Product of Vectors
*From*: "Adriano Pascoletti" <adriano.pascoletti at gmail.com>
*Date*: Sun, 25 May 2008 02:03:14 -0400 (EDT)
*References*: <200805240755.DAA20910@smc.vnet.net>
Gregory,this is a solution based on the listability of Times:
Total[X*Y, {2}] gives a list of length n.
Use List /@ Total[X*Y, {2}] to get an n x 1 array.
Adriano Pascoletti
On Sat, May 24, 2008 at 9:55 AM, Gregory Lypny <gregory.lypny at videotron.ca>
wrote:
> Hello everyone,
>
> 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.
>
> Regards,
>
> Gregory
>
>
>
>
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