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MathGroup Archive 2006

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Re: Quaternion problem

  • To: mathgroup at
  • Subject: [mg67415] Re: Quaternion problem
  • From: David Bailey <dave at>
  • Date: Thu, 22 Jun 2006 06:21:59 -0400 (EDT)
  • References: <e7ap5q$952$>
  • Sender: owner-wri-mathgroup at

Staffan Langin wrote:
> Hello,
> I'm a total Mathematica newbee so please bear with me :-). I'm trying to let 
> Mathematica analytically evaluate a second order derivative for me. The 
> function has several parameters with some of them being of 
> "Quaternion-type". I want to instruct Mathematica that the commutative rule 
> doesn't apply when evaluation the function. Is that possible? Thanks in 
> advance.
> Staffan Langin
The best way to do this is to use one of the built in operators with no 
definition - such as ** (NonCommutativeMultiply)  or \[CircleTimes] and 
then you can define it as you like. The properties of ordinary multiply 
- * or space - are assumed in too many places in Mathematica for it to 
be useful to think of changing these.

Although such an approach might seem a bit clumsy at first, it may 
ultimately be clearer to understand rather than ending up with 
complicated products, some of whose terms commute, and some of which don't.

David Bailey

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