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Re: Quaternion problem

• To: mathgroup at smc.vnet.net
• Subject: [mg67415] Re: Quaternion problem
• From: David Bailey <dave at Remove_Thisdbailey.co.uk>
• Date: Thu, 22 Jun 2006 06:21:59 -0400 (EDT)
• References: <e7ap5q$952$1@smc.vnet.net>
• Sender: owner-wri-mathgroup at wolfram.com

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
http://www.dbaileyconsultancy.co.uk