On Oct 4, 4:54 am, William Stein <wst...@gmail.com> wrote:
> On Sat, Oct 3, 2009 at 8:07 PM, Rob Beezer <goo...@beezer.cotse.net> wrote:
>
> > On Oct 3, 6:05 pm, William Stein <wst...@gmail.com> wrote:
> >> And this has already been almost completed by David Loeffler based
> >> on work by me. http://trac.sagemath.org/sage_trac/ticket/6449
>
> > The work at #6449 creates additive abelian groups by extending the
> > class for finitely-generated modules over ZZ. Assuming that approach,
> > is there a natural way to get all the subgroups?
>
> I don't think so. I have a hazy recollection that maybe a book by
> Henri Cohen on explicit class field theory has such an algorithm
> nicely described...
>
> > If so, I'm not
> > seeing it. Or would David Loeffler's routine for all subgroups of a
> > multiplicative abelian group need to be translated to the additive
> > version?
>
> Probably the latter.
>
> David Loeffler might want to comment, since I cc'd him.
>
>
>
> > Rob
>
> --
> William Stein
> Associate Professor of Mathematics
> University of Washingtonhttp://wstein.org
I wrote both the subgroups method of the old ab groups class and the
draft replacement class. The old subgroups method is essentially
secretly using the new approach under the hood -- it relies on the
Smith form routines for integer matrices -- so it would not be
difficult to translate the old code into the new framework. But it has
not been done so far.
The status of abelian groups in Sage at the moment is as follows. At
SD16 a project to revise abelian groups was announced; a number of
people voluteered to take part; a design discussion took place, and I
volunteered to write the first draft code; a few days later I had some
code working and I demoed this back to the group, feeling that I had
done my job and it was time for one of the five or six others who had
declared an interest in the project to take over; and since then the
code has sat there bitrotting on trac, and nothing has happened except
people sending me nagging emails attempting to persuade me to do yet
more work on it solo.
David
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