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MathGroup Archive 2006

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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


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