There is a related ticket out there about making character tables behave properly - that is to say, so that groups with identical character tables (such as isomorphic groups represented in different ways) can be identified. As pointed out below, that is easier said than done. But please let us know if anything can come out of this which could help with that!
- kcrisman On Jan 26, 8:01 am, Dima Pasechnik <dimp...@gmail.com> wrote: > David, > GAP does not fix an ordering of the conj. classes, or an ordering of > the irreducibles. They depend upon the way > the group comes in, and as conj. classes and irreds are often computed > by randomised procedures, > it's very hard to predict them. > (and not fun to deal with issues that somtimes arise due to this...) > > What is fixed, are these orderings in the character table library. > (and whenever applicable, they can be matched to the orderings used > in Atlas of Finite Groups (the big red book...)) > > Dima > > On Jan 26, 8:38 pm, David Joyner <wdjoy...@gmail.com> wrote: > > > > > On Tue, Jan 26, 2010 at 6:27 AM, Alex Ghitza <aghi...@gmail.com> wrote: > > > On Tue, 26 Jan 2010 06:19:16 -0500, David Joyner <wdjoy...@gmail.com> > > > wrote: > > > >> What Dima means is that the ordering returned by the character > > >> must of course agree with the internal ordering of the conjugacy classes. > > >> I assume (without having looked at your patch) that you are not > > >> changing the functions at all but only the doctests of the functions? > > >> Otherwise, you will somehow have to check that your character value > > >> ordering is "in sync" with the conjugacy class ordering. > > > > Ah, excellent. All I do is sort *the list of characters*, not the list > > > of values appearing in each character. (If you think of the character > > > table as having the characters listed as rows and conjugacy classes > > > listed as columns, I'm permuting the rows but leaving the columns > > > intact.) Does this make sense? (I've been staring at a laptop screen > > > for a bit too long today...) > > > Mathematically? Yes. > > To implement in Sage? I think it is it more complicated than that. > > > > I don't have the time to look into this at this very moment, so the rest > > > of this is speculation: we might want to give the same treatment to the > > > function that returns the list of conjugacy classes, to avoid similar > > > problems. That would mean that we're permuting the columns. Still, > > > we're doing the same operations across, so the table won't get "out of > > > sync", it will just be ordered differently. > > > You want the ordering of the characters to be consistent with the > > ordering of the conjugacy classes always. For most groups, there is > > no natural ordering but for some there are. My understanding is that > > you can't "fix" the ordering in any way you like unless you are at least > > sure that it preserves the ordering of groups for which a natural > > ordering exists (eg, the symmetric group). > > > My suggestion is to leave the ordering the way GAP (and I think > > also Magma) have fixed them. If you think that should change, for > > whatever reason, i think more GAP group people at least should > > be consulted on how to resolve the problem. However, if you just > > want to sort the output in the doctests (or even have a non-default > > "sorted" method added to the conj class and char functions, > > whcih would be a huge amount or work IMHO) then that is > > a different matter. > > > > Best, > > > Alex > > > > -- > > > Alex Ghitza -- Lecturer in Mathematics -- The University of Melbourne > > > -- Australia --http://www.ms.unimelb.edu.au/~aghitza/ > > > > -- > > > To post to this group, send an email to sage-devel@googlegroups.com > > > To unsubscribe from this group, send an email to > > > sage-devel+unsubscr...@googlegroups.com > > > For more options, visit this group > > > athttp://groups.google.com/group/sage-devel > > > URL:http://www.sagemath.org -- To post to this group, send an email to sage-devel@googlegroups.com To unsubscribe from this group, send an email to sage-devel+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/sage-devel URL: http://www.sagemath.org
