GiNaC and assumptions on variables?

[Parisse Bernard]

> 
> What you want to do doesn't sound impossible to me.  However, for my own
> part, I don't think I do need this kind of feature and so won't be able to
> help much.  Guidance is possible, though.  And no, nothing like this has
> been implemented yet.
> 
> Adding assumptions to expressions throws up a couple of questions: Where
> do you stick assumption-tags?  A pointer to something in class ex might
> slow it down somewhat, though this needs to be tested.  I think ex would
> be the way where to store it.  The alternative would be a protected
> variable in class basic.  You need to think about how to evaluate those
> tags.  The trivial example you give suggests that each class' eval()
> function should check for members' property-tags, it could read them via
> the .info() method.  (The info_flags class might need some careful
> restructuring, if this wants to be going into production use.  It is
> pretty much hacked together.)  If it gets in the way in the .eval()
> function, an alternative would be to add this checking to another
> evaluation-method.  It can soon get very involved as soon as more than one
> variables are involved.  There is some literature about this and one
> should carefully check what Maple does here.

The main algorithm I know works on polynomial: for univariate
polynomials,
it is known as Sturm sequence. For multivariate polynomials (systems)
I believe it is still an active reseach field (search for example
for publications of M.-F. Roy), technics involved are Sturm sequences
generalizations and Groebner basis (BTW, implementing Groebner basis is
one of my objective with my polynomial classes).