https://github.com/sagemath/sage/issues/36780
On Saturday, 25 November 2023 at 15:11:53 UTC John Cremona wrote: > Thanks for this report, which certainly indicates a bug. I will look into > it as the code here was written by me. I note that the two curves have CM > (by the order of index 5 and the maximal order in Q(sqrt(-3)) > respectively), and the code to deal with isogenies is different in this > case. The relevant function is isogeny_degrees_cm(), imported > from sage.schemes.elliptic_curves.isogeny_class. And for some reason that > function is not including the valid isogeny prime 5. > > If you do F.isogeny_class(reducible_primes=[3,5]) you get the same as for > E (but you have to so that in a fresh Sage session becauses of caching of > previously computed results). > > John Cremona > > On Friday, 24 November 2023 at 03:50:54 UTC hbetx9 wrote: > >> Hi, >> >> In some work on isogeny clases, my team ran across the following of two >> elliptic curves which are isogenous but sage reports different isogeny >> classes for them. Is there some technicalities (j = 0) leading to >> incorrect output or is this something that we should flag a bug? >> >> sage: L5.<r5> = NumberField(x^2-5) >> >> sage: E = >> EllipticCurve(L5,[287275052073119826051072\*r5-642366544675288047943680,-125329261653845158603060848774610944\*r5+280244748627855491701953075326484480]) >> >> sage: F = EllipticCurve(L5,[0,-4325477943600\*r5-4195572876000]) >> >> sage: E.isogeny_class().matrix() >> [ 1 25 75 3 5 15] >> [25 1 3 75 5 15] >> [75 3 1 25 15 5] >> [ 3 75 25 1 15 5] >> [ 5 5 15 15 1 3] >> [15 15 5 5 3 1] >> >> sage: F.isogeny_class().matrix() >> [1 3] >> [3 1] >> >> sage: E.is_isogenous(F) >> True >> >> Best, >> Lance >> > -- You received this message because you are subscribed to the Google Groups "sage-support" group. To unsubscribe from this group and stop receiving emails from it, send an email to sage-support+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/sage-support/ec0aba44-faaf-4bb0-a5d4-e6bd027131a5n%40googlegroups.com.
