On Thu, 31 Aug 2023 at 15:00, John Cremona <[email protected]> wrote:
> Thanks for the report, you are correct and there is a bug in the code. > When reducing the cusp 6/7 it first reduced 6 and 7 mod the level 7 to get > 6 and 0, then calls an internal function _lift_pair() which assumes that > the new pair of integers is coprime. > In fact the bug was slightly different: after reducing u and v mod N (for the cusp u/v) when v=0 it was only returning Infinity (1/0) when u=1, not also when u=N-1. I'll make a PR for this soon. > > I will raise an issue and (probably) fix it right away. > > John > > On Thu, 31 Aug 2023 at 08:06, Ralf Hemmecke <[email protected]> wrote: > >> The following contradicts the specification of reduce_cusp for Gamma(7). >> >> >> https://doc.sagemath.org/html/en/reference/arithgroup/sage/modular/arithgroup/congroup_gamma.html >> >> sage: Gamma(7).are_equivalent(Cusp(6,7),Cusp(1,0)) >> True >> sage: Gamma(7).reduce_cusp(Cusp(1,0)) >> Infinity >> sage: Gamma(7).reduce_cusp(Cusp(6,7)) >> 6/7 >> >> Ralf >> >> -- >> 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 [email protected]. >> To view this discussion on the web visit >> https://groups.google.com/d/msgid/sage-devel/ebffabc9-b0c8-656e-aab5-e769057dfe18%40gmail.com >> . >> > -- You received this message because you are subscribed to the Google Groups "sage-nt" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To view this discussion on the web visit https://groups.google.com/d/msgid/sage-nt/CAD0p0K71fB8Hh3H0D67WvcURZ52H_2iKO%3DfjcZ5_UjrM0b54AQ%40mail.gmail.com.
