#14019: equality is broken for Posets
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Reporter: ncohen | Owner: sage-combinat
Type: defect | Status: needs_info
Priority: major | Milestone: sage-5.13
Component: combinatorics | Resolution:
Keywords: | Merged in:
Authors: Nathann Cohen | Reviewers:
Report Upstream: N/A | Work issues:
Branch: | Commit:
u/andrew.mathas/ticket/14019 | a1a85ff09dcc34a56b9362a9d4461d907296718e
Dependencies: | Stopgaps: #14185
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Comment (by ncohen):
Hmmmmmm... Must be because my original patch fixed several things, and two
of these fixes are not compatible with each other : I also made
`.hasse_diagram()` return a `HasseDiagram` object.
In the patch you imported with git, this modification is not made anymore.
So you compare `DiGraph` objects, and not `HasseDiagram` objects. Perhaps
it still works if you compare the results of `.hasse_diagram()` instead of
`._hasse_diagram` directly.
Arggggggg ! No, I think I understood ! I think that it is incorrect to
compare the `._hasse_diagram` digraphs, because they are always labelled
with integers, so when you do that you do not compare the vertice' labels
:
{{{
sage: list(posets.IntegerCompositions(3))
[[3], [1, 2], [2, 1], [1, 1, 1]]
sage: list(posets.IntegerCompositions(3).hasse_diagram())
[[3], [1, 2], [1, 1, 1], [2, 1]]
sage: list(posets.IntegerCompositions(3)._hasse_diagram)
[0, 1, 2, 3]
}}}
And of course as you compare digraphs defined on integers there is no
problem, for they don't have parents. But it may say that two posets are
equal even if they are defined on disjoint sets of elements.
Nathann
--
Ticket URL: <http://trac.sagemath.org/ticket/14019#comment:26>
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