Maxima doesn't assume ommutativity? (bug?)

Daniel,

The problem that you describe here is related with the "expand". Looks
like there is a problem with expand when you are making some "real
stuff". So try with "ratexpand" or "rat" commands instead. This is the
behavior whit rat when I use the input of your example:

(C1) rat((-A^3*a/64+a*A^3/64));
(D1)/R/ 				   0

Seems good isnt it? ;-)

Hope this help.

Cheers,

Offray Vladimir

On dom, 2002-02-03 at 14:17, Daniel Lemire wrote:
> Good day,
> 
> The example I gave was too simple. Yes, a*b-b*a does simplifies to 
> zero... but see the slightly more challenging problem below...
> 
> Do you feel I should report this as a bug or am I being silly??? Please, 
> someone, do a sanity check on me! It seems to me that Maxima doesn't 
> assume commutativity!!!! (why???)
> 
> 
> 
> [lemire@romeo lemire]$ maxima
> GCL (GNU Common Lisp)  Version(2.5.0) jeu jan 31 23:03:22 EST 2002
> Licensed under GNU Library General Public License
> Contains Enhancements by W. Schelter
> Maxima 5.6 jeu jan 31 23:03:13 EST 2002 (with enhancements by W. Schelter).
> Licensed under the GNU Public License (see file COPYING)
> (C1) expand((-A^3*a/64+a*A^3/64));
> 
>                                       3    3
>                                    a A    A  a
> (D1)                              ---- - ----
>                                     64     64
> (C2) scsimp(D1);
> 
>                                       3    3
>                                    a A    A  a
> (D2)                              ---- - ----
>                                     64     64
> (C3)
> 
> 
> This type of bug crept up on my as I was doing some "real" research 
> using Maxima. I had a conjecture that such polynomial and such other 
> polynomial would simplify in such a way that... (skip details)... but I 
> spent (wasted) a day with very complicated formulas until a realized 
> that Maxima didn't assume commutativity!!! So that even though I 
> strongly suspected that things would greatly simplify, they apparently 
> did not!
> 
> Of course, here I give a rather simple examples, but it happened to me 
> several times over the last few weeks, involving various complicated 
> expressions. This one was the simplest I could find.
> 
> This problem seems to happen systematically, but is somewhat random at 
> the same time (that is, I can't tell from the expression whether this 
> bug will happen... but once it happens for a certain expression, if I 
> have this expression with other terms, the problem with happen! Hence, 
> it is systematical...)
> 
> I've recently upgraded my lisp. It didn't fix the problem for me.
> 
> I have
> Linux  2.4.2-2 with a 686
> 
> Maxima built from cvs using latest lisp (from cvs). The problem happened 
> to me on the maxima RPM though.
> 
> I can't believe I would be the first one to notice this problem???
>