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MathGroup Archive 1993

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matrices

  • To: mathgroup at yoda.physics.unc.edu
  • Subject: matrices
  • From: Cetin Cetinkaya <cetin at acm0.me.uiuc.edu>
  • Date: Tue, 30 Mar 1993 14:18:10 -0600

I am planning to do some perturbation analysis for the equations which involves
matrices and scalars. My question is simple: Is there any way to have MMA to
distingush matrices form scalars and vice versa? Let me give an example to make
the question clearer:

Let A and B be matrices of the same dimensions and let eps to be a scalar.
To calculate (A + eps B)^2, in MMA I can write:


In[124]:= A=.;B=.;Distribute[(A + eps B).(A + eps B)]
0. Second  2163.248 KByte

Out[124]= A . A + A . (B eps) + (B eps) . A + (B eps) . (B eps)  

But I would like to collect the terms with respect to eps, that is, the form 
I want is:

A.A + eps ( A.B + B.A ) + eps^2 B^2.

I have tried Collect[], of course it did not work,

In[125]:= Collect[%,eps]
0. Second  2163.696 KByte

Out[125]= A . A + A . (B eps) + (B eps) . A + (B eps) . (B eps)

If MMA could see the difference between a matrix and a scalar, this could have 
been possible, I think. 

Thank you in advance,

cetin







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