Hi John, Thanks a bunch for the pointed reply. Glad to hear we weren't missing something easy and thanks a bunch for filling the bug report!
Best, Lance On Sunday, November 26, 2023 at 10:16:53 AM UTC-6 John Cremona wrote: > 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/a9f5672f-407e-4a51-8ee4-fbb5ddad3c35n%40googlegroups.com.
