[with patch, needs review] make abelian group list/iter and classgroup list/iter more modern

Needs work. Your fix patch introduces a bug:

sage: G = AbelianGroup([2,3], names = "ab") sage: v = G.list()
sage: v
[1, b, b^2, a, a*b, a*b^2]
sage: v[0] = "hi nick!"
sage: G.list()
['hi nick!', b, b^2, a, a*b, a*b^2]

3810-ncalexan-abelian-group-iter-2.patch replaces 3810-ncalexan-abelian-group-iter.patch and addresses referee comment.

This is functionality which I wanted a few days ago so I am pleased to see this ticket!

I applied 3810-ncalexan-abelian-group-iter-2.patch and then 3810-ncalexan-class-group-list.patch in that order. When Sage applied the second one I was surprised that it popped up an edit window as when one does a commit. I just closed the window.

So I don't really know what it was I tested, but it seemed to work as advertised (and without the bug William pointed out).

Here's an enhancement I would like: If I create an ideal class from some random ideal, nothing really happens, and I cannot tell which class I got without testing for equality with every class. Am I missing something? I actually would have been happy to have class group elements display as abstract group elements (as they would in Magma), as long as functions were provided to go from fractional ideals to abstract ideal classes and back again.

With the two patches John mentioned I get the following doctest failure:

sage -t -long devel/sage/sage/rings/number_field/class_group.py
**********************************************************************
File "/scratch/mabshoff/release-cycle/sage-3.1.2.alpha1/tmp/class_group.py", line 117:
    sage: list(G)
Expected:
    [Trivial principal fractional ideal class, Fractional ideal class (2, 1/2*a^2 + a - 1/2), Fractional ideal class (2, 1/2*a^2 + 1/2)]
Got:
    [Trivial principal fractional ideal class, Fractional ideal class (2, 1/2*a^2 - a + 3/2), Fractional ideal class (2, 1/2*a^2 + 1/2)]
**********************************************************************
File "/scratch/mabshoff/release-cycle/sage-3.1.2.alpha1/tmp/class_group.py", line 119:
    sage: G.list()
Expected:
    [Trivial principal fractional ideal class, Fractional ideal class (2, 1/2*a^2 + a - 1/2), Fractional ideal class (2, 1/2*a^2 + 1/2)]
Got:
    [Trivial principal fractional ideal class, Fractional ideal class (2, 1/2*a^2 - a + 3/2), Fractional ideal class (2, 1/2*a^2 + 1/2)]
**********************************************************************

The reason that trac_3810-ncalexan-class-group-list.patch popped up a window is that it is a straight diff instead of a patch. Nick: Can you post a unified patch and delete the old ones?

Cheers,

Michael

Those doctest differences are insignificant in that the output is mathematically identical to what is expected. For deterministic output we need (as well as the usual sorting): the same ideals representing each class, and the same presentation of each ideal. Here it's just that the second ideal in the list has a different second generator.

My understanding is that these generators come from pari. If so, it is probably safe to replace the doctest output with the new output. Perhaps Nick could say if that sounds right to him.

Nick, any news on this? It might be relevant to #4061 which I am about to post a patch for.

I think these should be applied. The doctest output should be updated, but I don't have the original patch queue anymore to give a non-patch.