Re: Re: Can't multiply non-square matrices.

*To*: mathgroup at smc.vnet.net*Subject*: [mg64623] Re: [mg64570] Re: Can't multiply non-square matrices.*From*: Murray Eisenberg <murray at math.umass.edu>*Date*: Fri, 24 Feb 2006 00:18:20 -0500 (EST)*Organization*: Mathematics & Statistics, Univ. of Mass./Amherst*References*: <dthgr4$n74$1@smc.vnet.net> <200602230534.AAA13114@smc.vnet.net>*Reply-to*: murray at math.umass.edu*Sender*: owner-wri-mathgroup at wolfram.com

Of course {a, b} does not really represent a matrix, as it has only a single dimension, whereas {{a, b}} does represent a matrix, namely, a one-row matrix. Jens-Peer Kuska wrote: > Hi, > > {a, b}.{{c}, {d}} > > ?? > > the usual Times[] * does an element-wise multiply. > > Regards > > Jens > > > "Chris Young" <c1572young at earthlink.net> schrieb > im Newsbeitrag news:dthgr4$n74$1 at smc.vnet.net... > | Is there a way to multiply non-square matrices? > E.g., a 3-row by 2-row > | matrix times a 2-row by 1-row matrix should > yield a 3-row by 1-row > | matrix, if I remember my linear algebra > correctly. > | > | Instead when I do something like > | > | (a b) (c) > | (d) > | > | I get an error involving "Thread::tdlen": > | > | Thread::tdlen: Objects of unequal length in {{a, > b}}\{{c}, {d}} cannot be \ > | combined. > | > | (The "(c)" and "(d)" above represent a > 2-dimensional column vector, > | with one pair of parenthese around them.) > | > | I entered the line > | << LinearAlgebra`MatrixManipulation` > | but this doesn't seem to help. > | > | Any help appreciated. > | > | Chris Young > | > > > -- Murray Eisenberg murray at math.umass.edu Mathematics & Statistics Dept. Lederle Graduate Research Tower phone 413 549-1020 (H) University of Massachusetts 413 545-2859 (W) 710 North Pleasant Street fax 413 545-1801 Amherst, MA 01003-9305

**References**:**Re: Can't multiply non-square matrices.***From:*"Jens-Peer Kuska" <kuska@informatik.uni-leipzig.de>