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MathGroup Archive 1998

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Re: RE: Re: Re: Non-comm

  • To: mathgroup at smc.vnet.net
  • Subject: [mg13446] Re: [mg13414] RE: [mg13344] Re: [mg13280] Re: Non-comm
  • From: MJE <evans.nospam at gte.net>
  • Date: Fri, 24 Jul 1998 01:45:34 -0400
  • Organization: None
  • References: <199807230733.DAA05517@smc.vnet.net.>
  • Sender: owner-wri-mathgroup at wolfram.com

Hi Ted -

Regarding NonCommutativeMultiply:

This feature doesn't solve any of the problems I mentioned.  As a
trivial example, write 'NonCommutativeMultiply[I,A]' where 'I' is meant
to represent the identity matrix.  You can't tell Mathematica that I
and A are matrices, much less that I is the identity matrix, without
defining the full-blown forms.  Mathematica assumes that I and A
represent complex numbers.  So the matrix expression 'I A' will not
simplify under NonCommutativeMultiply.

Your comment about the Notation package is true in general terms, but
for common things like symbolic matrix math, WRI should write the rule
base, not every user on his own.

Mark


Ersek_Ted%PAX1A at mr.nawcad.navy.mil wrote:
> 
> Isn't this built-in as a different type of multiplication?
> 
> In[5]:=
> ?NonCommutativeMultiply
> 
> "a ** b ** c is a general associative, but non-commutative, form of \
> multiplication."
> 
> If you like you can use the Notation package to define a convention for
> Input and/or Output that is more readable.
> 
> Ted Ersek
>



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