#18383: Coercion and comparison for alternating sign matrices
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Reporter: vdelecroix | Owner:
Type: enhancement | Status: needs_work
Priority: major | Milestone: sage-6.7
Component: combinatorics | Resolution:
Keywords: | Merged in:
Authors: Vincent Delecroix | Reviewers:
Report Upstream: N/A | Work issues:
Branch: | Commit:
u/vdelecroix/18383 | 390e2d7cf57899cde4c7b096ef5b97f0be909574
Dependencies: | Stopgaps:
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Comment (by tscrim):
Replying to [comment:18 vdelecroix]:
> Replying to [comment:17 tscrim]:
> > For rich comparisons, yes. However for `cmp`, the code path currently
completely bypasses the rich comparisons because it calls `__cmp__` (which
calls `_cmp` which calls `_cmp_` and errors out).
>
> This has been fixed in #18322.
If that does have the rich comparisons in the code path, then it should
fix the issue without having to define a `_cmp_`.
> > > Do you have an example involving rich comparisons that differ?
>
> > I'm not sure what you're asking for.
>
> I wanted an example of a comparison that is different before and after
my branch.
Here is one:
{{{
sage: ASM = AlternatingSignMatrices(3)
sage: x = ASM[3]
sage: x
[ 0 1 0]
[ 1 -1 1]
[ 0 1 0]
sage: x < matrix.identity(3) # True with this branch
False
}}}
and it is because the coercion framework gets involved. Although ASM's
only have the inequality comparisons for plotting due to the digraph
calling `sorted` in `vertices()` which fails (#15372, which was a quick
hack around the problem IMO) rather than just choosing some order. So the
inequality comparisons are not mathematically defined as-is (even for
matrices IMO, where they are just considered as 2-dim arrays). So now I'm
completely convinced they should be rewritten to use the lattice.
--
Ticket URL: <http://trac.sagemath.org/ticket/18383#comment:19>
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