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/26785a33-7be4-4682-b988-ec2a4452a8a4n%40googlegroups.com.
