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nested * and ** (rules for commutative quantities)

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  • Subject: [mg7658] nested * and ** (rules for commutative quantities)
  • From: mabi at (Marlies Brinksma)
  • Date: Thu, 26 Jun 1997 01:36:45 -0400 (EDT)
  • Sender: owner-wri-mathgroup at

Hello everybody,

I'm having the following problem.

I have a set of operators (let's call them Op[index_,arg2_]).
Two of these operators commute when their indices are different and they are 
noncommutative otherwise. All operators commute with any scalar quantity.

I would like to define some rules such that expressions like:

Op[3,a] ** Op[2,v] ** 4 ** Op[6,s] ** Op[2,x] ** Op[1,t]

will be automatically changed to:

Times[4, Op[1,t],NonCommutativeMultiply[Op[2,v],Op[2,x]],Op[3,a],Op[6,s]]

It seems to be very simple but I just cannot come to a set of rules which are
general enough and don't lead to infinite recursion.

Can anyone please help me?

Thanks in advance for any help!

Marlies Brinksma

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