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[Axiom-developer] Commutative symbols was: Re: Limits in Axiom

From: Ralf Hemmecke
Subject: [Axiom-developer] Commutative symbols was: Re: Limits in Axiom
Date: Mon, 26 Mar 2007 12:51:01 +0200
User-agent: Thunderbird 2.0b2 (X11/20070116)

However, I must say that your expression approach is limited in the
sense that it can only deal with commuting objects. Simplifying b*a+a*b
to 2*a*b is not correct if b is the differentiation operator D on x and
a=X is the "multiplication by x"-operator. Then you would have D*X=X*D+1.

Of course. Try in SymPy:

In [2]: x*y+y*x
Out[2]: 2*y*x

In [10]: a = Symbol("a", is_commutative=False)

In [11]: b = Symbol("b", is_commutative=False)

Hmmm, I would have thought that commutativity is a property of the multiplication of the domain you are working in and not a property of a symbol.


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