On Tue, Aug 30, 2016 at 8:45 AM, Vincent Delecroix <20100.delecr...@gmail.com> wrote: > Hi Ralf, > > First of all, your opinon is more valuable than others since you are the > maintainer of Pynac.
Perhaps my opinion is also worth something since I made up the name "Pynac" and wrote the first version of Pynac.... William > > That being said, the constraint specification of symbolic variables in Sage > is really poor. Ideally, we should be able to have symbolic computation more > tightly linked to Sage parents. It should involve some kind of coercion > under the hood and raise error when the operation is not appropriate. > > For example > > sage: x = SR.variable(domain = GF(3)) > sage: n = SR.variable(domain = ZZ) > sage: x^n + 1 # coercion: 1 is converted to GF(3) > x^n + 1 > sage: x^3 # automatic simplification > x > sage: x + n # the domain of n becomes GF(3) > sage: (x + n)^3 # automatic simplification > x + n > sage: cos(x) # does not make sense > Traceback (most recent call last): > ... > ValueError: undefined > > However, for non-exact rings we might want to forbid the coercion, e.g. as > in "pi + 1.0". But even in this case the expression is well identified as > being "real". > > In particular (and answering your question :-) > > - in a single expression I would forbid the mix of elements which belong to > rings with different characteristic, unless it is an operation associated to > a valid coercion in Sage (e.g. GF(3) and ZZ) > > - I would associate to each symbolic expression a domain (i.e. set of > numbers with constraints) that would define a set of available operations > > Best, > Vincent > > > On 30/08/16 12:28, Ralf Stephan wrote: >> >> As you know Pynac provides symbolic computation. In earlier times >> this included polynomial manipulation and other things where Sage >> has now dedicated and consistent algebraic structures. Pynac nowaday >> is mostly calculus. For this reason, and because I'm tired of trying to >> fix >> things that belong in other parts of Sage I propose to make it an error >> to mix elements of rings with positive characteristics (or symbolic Mod) >> and symbolic variables. >> >> The error could also hint at a solution using the resp. polynomial rings. >> >> I don't think there is much interest in the mentioned feature atm, because >> the present behaviour IS already buggy, and no one complained. >> But maybe I'm completely wrong, please state your opinion. >> >> Regards, > > > -- > You received this message because you are subscribed to the Google Groups > "sage-devel" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to sage-devel+unsubscr...@googlegroups.com. > To post to this group, send email to sage-devel@googlegroups.com. > Visit this group at https://groups.google.com/group/sage-devel. > For more options, visit https://groups.google.com/d/optout. -- William (http://wstein.org) -- You received this message because you are subscribed to the Google Groups "sage-devel" group. To unsubscribe from this group and stop receiving emails from it, send an email to sage-devel+unsubscr...@googlegroups.com. To post to this group, send email to sage-devel@googlegroups.com. Visit this group at https://groups.google.com/group/sage-devel. For more options, visit https://groups.google.com/d/optout.
