I agree, which is why I supported making some sort of canonical_comparison method for output, and then using <= for subgroup.
On Fri, May 23, 2008 at 11:36 AM, John Cremona <[EMAIL PROTECTED]> wrote: > > Following on from Nick's point, I cannot imagine that users will want > or expect to sort a list of groups except possibly by some criterion > provided by the user (e.g. size of the group, or something). But > apart from that we need to be able to have a default sorting or more > or less anything in Sage so that we can have consistent output where > possible and meaningful. > > John > > 2008/5/23 David Joyner <[EMAIL PROTECTED]>: >> >> I agree with Nick and John. >> >> On Fri, May 23, 2008 at 12:45 PM, Robert Miller <[EMAIL PROTECTED]> wrote: >>> >>> Hello, >>> >>> During the last bug day, I found several tickets related to >>> inconsistencies in abelian groups. I think I've fixed the circular >>> logic, etc. causing the problems in the patch included in #1284. >>> However, there is a difference of opinion on notation that I need to >>> ask about here. >>> >>> Q: Should the output of >>> sage: G <= H >>> for G and H abelian groups be whether G is a subgroup of H? >>> >>> I know the answer seems simple, but here's why you might want to >>> answer no (William suggested this to me). If you have a list of >>> abelian groups L = [G1,...,Gn], and you want to quickly sort it, if >>> you do sorted(L), you may not get back what you are expecting, since >>> the subgroup ordering on abelian groups isn't linear. >>> >>> gfurnish proposes the alternative sorted(L, >>> cmp=canonical_ab_group_cmp), with G <= H returning whether G is a >>> subgroup of H. I think I favor this approach. >>> >>> The other option is G.is_subgroup(H). >>> > >>> >> >> > >> > > > > --~--~---------~--~----~------------~-------~--~----~ 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-devel URLs: http://www.sagemath.org -~----------~----~----~----~------~----~------~--~---
