I agree: composition of power series should only be allowed when the "inner" one has positive valuation, i.e. zero constant term. (At least over an integral domain. Maybe it's ok if the constant term is just a zerodivisor, but I cannot think of a situation where that would be needed!)
It would be quite fun to implement the Nottingham Group which (for each prime p) is the group of power series over F_p with zero constant term, under composition. This is of great interest to a wide range of number theorists and group theorists. But I am not an expert. John On Feb 25, 11:06 am, Ralf Hemmecke <r...@hemmecke.de> wrote: > > Yes, this is a bug. The result should be O(z^0), just as in the > > following example: > > > sage: S.<z> = QQ[[]] > > sage: p = 1 + z + O(z^2) > > sage: q = 1 + z > > sage: p(q) > > O(z^0) > > > This is now trac #5367. > > Are you sure that O(z^0) is correct? > x = 1 + z + z^2 + z^3 + ... (ad infinitum) > would be a series that fits in the class p. > Now plug in q. Sounds as infinity (which is the the constant term of the > result) is O(z^0)... > > I would rather forbid the constant term of q to be anything but zero. > > I guess the sage-combinat people probably have something to say here. > > Ralf --~--~---------~--~----~------------~-------~--~----~ To post to this group, send email to sage-devel@googlegroups.com To unsubscribe from this group, send email to sage-devel-unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/sage-devel URLs: http://www.sagemath.org -~----------~----~----~----~------~----~------~--~---
