ratsubst depends on the CRE representation, which represents everything as
a (commutative) rational function, e.g.
exp(2*x)+exp(-x)+x^3/3
is treated as
(3*Y^3+(1*X^3)*Y^1+3*Y^0) / (3*Y) where Y=%e^x and X=x
This doesn't generalize in any sensible way I can see to the
non-commutative case.
You could imagine ratsubst-like functionality for non-commutative products,
but it would essentially have to be written from scratch. By the way,
what would you do with
ncsubst( q , b . a , a^^-1 . b^^3 . a )
=> a^^-1 . b^^2 . q
=> ( a^^-1 . q ) ^^3
-s
On Mon, Oct 8, 2012 at 2:44 PM, Barton Willis <willisb at unk.edu> wrote:
> > Obviously, another approach for easy examples like this is something like
> > (%i1) e : a.b.c$
> > (%i2) subst(c^^(-1), b, e);
> > (%o2) a
> > I actually use this idea quite a lot (for commutative expressions) when
> > I don't want ratsubst to mess up the structure of the expression.
>
> > Rupert
>
> That's cute--never would have thought of that---I was aiming for an ad-hoc
> method, not some grand general scheme
> (but I think ratsubst should be able to handle the some easy cases).
> Thanks,
>
> Barton
>
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