That's fair enough, especially in the case where you are comparing A with a subgroup of itself.
John 2008/5/8 Utpal Sarkar <[EMAIL PROTECTED]>: > > I think it should be considered a bug, because it is sage, not the > user, that decides what presentation to use. In this example, the > group A is not considered equal to the subgroup generated by its > generators (groups that are not only isomorphic, but really equal), > because internally the presentation of the subgroup differs from that > of the ambient group. > On the other hand, there are isomorphic groups with different > presentations that are considered equal: > AbelianGroup([6]) == AbelianGroup([1,6]) > True > > > > > On May 8, 10:16 am, "John Cremona" <[EMAIL PROTECTED]> wrote: > > Is this actually a bug? It would certainly wrong if the test being > > performed was isomorphism rather than equality, but I think it is > > actually reasonable for two finite abelian groups to only be reported > > as "equal" when they are presented the same way. > > > > John Cremona > > > > 2008/5/7 William Stein <[EMAIL PROTECTED]>: > > > > > > > > > > > On Wed, May 7, 2008 at 3:18 PM, Utpal Sarkar <[EMAIL PROTECTED]> wrote: > > > > > > Hi there, > > > > > > When I define an abelian group > > > > A = AbelianGroup(1,[6]) > > > > and then generate a subgroup that actually is the whole group itself, > > > > and then compare it to the original group: > > > > A.subgroup(list(A.gens())) == A > > > > the result may be either True or False. In this example it is False. > > > > When defining A as > > > > A = AbelianGroup(2,[3,2]) > > > > it is False as well, but when I define it as > > > > A = AbelianGroup(2,[2,3]) > > > > it is True. > > > > My guess is that this is because comparison of finite Abelian groups > > > > is implemented using their invariant factors, but when you create the > > > > group using factors that are not in canonical form or not in > > > > increasing order, these are used instead of the ordered list of > > > > invariant factors anyway. > > > > > > Greetings, > > > > > > Utpal > > > > > Thanks for reporting this bug! We are tracking it here: > > > > > http://trac.sagemath.org/sage_trac/ticket/3127 > > > > > -- William > > > --~--~---------~--~----~------------~-------~--~----~ To post to this group, send email to [email protected] To unsubscribe from this group, send email to [EMAIL PROTECTED] For more options, visit this group at http://groups.google.com/group/sage-support URLs: http://www.sagemath.org -~----------~----~----~----~------~----~------~--~---
