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 > > > >

**References**:**Dot Product of Vectors***From:*Gregory Lypny <gregory.lypny@videotron.ca>