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MathGroup Archive 1995

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Re: How to simplify transposed terms?

  • Subject: [mg2720] Re: How to simplify transposed terms?
  • From: rubin at msu.edu (Paul A. Rubin)
  • Date: Sat, 9 Dec 1995 01:55:47 -0500
  • Approved: usenet@wri.com
  • Distribution: local
  • Newsgroups: wri.mathgroup
  • Organization: Michigan State University

In article <49do0r$8a6 at dragonfly.wri.com>,
   Bernd.Cebulski at e-technik.tu-chemnitz.de (Bernd Cebulski) wrote:
->How could I tell MMA to simplify
->
->Transpose[A*B] --->  Transpose[B]*Transpose[A]
->Transpose[A+B] --->  Transpose[A]+Transpose[B]
->
->And how could I declare 'A' as a matrix without giving values to it, so 
that
->calculations like the 2 examples could be made. Of course they should be 
a 
->little more complicated ...
->
->Tnx, 
->
->	Bernd.
->
-> -----------------------------------------------.
->|     Chemnitz, University of Technology        |
->|--- bernd.cebulski at e-technik.tu-chemnitz.de ---|
->|            Phone: +49 (371) 5313318           |
->|            Fax:   +49 (371) 5313361           |
->|                   DL 1 DTP                    |
->`------------------------------------------------

First step, unprotect Transpose and add the desired properties:

  Unprotect[Transpose];
  Transpose[ A_ B_ ] := Transpose[ B ] Transpose[ A ] /;
    MatrixQ[ A ] && MatrixQ[ B ]
  Transpose[ A_ + B_ ] := Transpose[ A ] + Transpose[ B ] /;
    MatrixQ[ A ] && MatrixQ[ B ]
  Protect[ Transpose ];

Note that I've restricted the properties to apply only when both arguments 
are recognizable as matrices.  (You could also do this with the alternate 
notation 
  Transpose[ A_?MatrixQ B_?MatrixQ ] := Transpose[ A ] Transpose[ B ]
and similarly for distribution across addition.)

The next step is to define symbols to be matrices using up-values.  Note 
that for undefined A and B, the properties are not invoked:

  In[]:= Transpose[ A B ]
  Out[]= Transpose[A*B]
  In[]:= Transpose[ A + B ]
  Out[]= Transpose[A + B]

But if we define A and B to be matrices then the properties are applied:

  In[]:= A /: MatrixQ[ A ] := True
  In[]:= B /: MatrixQ[ B ] := True
  In[]:= Transpose[ A B ]
  Out[]= Transpose[A]*Transpose[B]
  In[]:= Transpose[ A + B ]
  Out[]= Transpose[A] + Transpose[B]

Hope this helps.

Paul

**************************************************************************
* Paul A. Rubin                                  Phone: (517) 432-3509   *
* Department of Management                       Fax:   (517) 432-1111   *
* Eli Broad Graduate School of Management        Net:   RUBIN at MSU.EDU    *
* Michigan State University                                              *
* East Lansing, MI  48824-1122  (USA)                                    *
**************************************************************************
Mathematicians are like Frenchmen:  whenever you say something to them,
they translate it into their own language, and at once it is something
entirely different.                                    J. W. v. GOETHE


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