*To*: mathgroup@smc.vnet.net*Subject*: [mg11835] Re: commutativity*From*: David Annetts <dannetts@laurel.ocs.mq.edu.au>*Date*: Wed, 1 Apr 1998 00:35:41 -0500*Organization*: CRCAMET/Macquarie University*References*: <6ek4j9$jag@smc.vnet.net> <6fd237$5u9@smc.vnet.net> <6fo47n$ock$7@dragonfly.wolfram.com>

> Hi, > > Daitaro Hagihara wrote: > > > In article <6ek4j9$jag@smc.vnet.net>, John Albert Horst > > <horst@cme.nist.gov> wrote: > > > > > I would like to be able to define a rule called, say, commutativeOff > > > that would work as follows: > > > > > > In[1] := a*b == b*a/.commutativeOff > > > > > > Out[1] := False > > > > > > As it is, > > > > > > In[1] := a*b == b*a > > > > > > Out[1] := True > > > > > > How can I do this? > > > > Working on this topic on and off for a week, I came up with a poor man's > > non-commutative package. It uses ordinay symbols to represent basic > > algebra, and it can be turned on and off by a couple of switches in a > > considerately unintrusive way. Just eval all of the following in > > brackets ([...]), and it starts out with the usual commutative > > behavior; all math is unchanged. Then by issuing "commutativeOff" > > command, things will become completely non-commutative. To get back to > > the usual behavior, issue "commutativeOn" command. The vector > > differentiation is currently nothing more than a hack. Even with a > > future improvement, if any, this is no replacement for full tensor > > packages out there. A thousand apologies for the empty message:( What I intended to say, was that I recall a MathSource package called NonCommutativeAlgebra, that looks like a Rich man's package -- ================================================================== David Annetts _____________ http://www.ocs.mq.edu.au/~dannetts/ |C R C A M E T| * Ban all Multi-line signature files * |-------------| Banning Systems Administration in 1998 when at |_____ | CRC for Australian Mineral |````` \ | Exploration Technologies |`````/$\ | Earth Sciences |````/$$$\____| Macquarie University, NSW 2109 |```/$$$/.....| AUSTRALIA |``/$$$/......| phone: +(1-61-2) 9850 9280, fax (1-61-2) 9850 8366 ------------- ==================================================================