#14019: equality is broken for Posets
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Reporter: ncohen | Owner: sage-combinat
Type: defect | Status: needs_info
Priority: major | Milestone: sage-6.4
Component: combinatorics | Resolution:
Keywords: | Merged in:
Authors: Nathann Cohen | Reviewers:
Report Upstream: N/A | Work issues:
Branch: | Commit:
u/andrew.mathas/ticket/14019 | d10a6efa75561632cdc76b2c98c5eca4312372ec
Dependencies: | Stopgaps: #14185
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Comment (by tscrim):
`relabel()` does return a new poset. The issue is a little more subtle in
regards to the ordering on the set of elements of the poset:
{{{
sage: list(p1)
[3, 2, 1]
sage: list(p2)
[2, 3, 1]
}}}
because
{{{
sage: p1._elements
(3, 2, 1)
sage: p2._elements
(2, 3, 1)
}}}
That is why they don't compare as equal (as it is part of the construction
data). The simplist change (FTR, I don't consider this to be a bug, but
instead a lack of documentation) would be to make the Hasse diagram the
only part of the construction info, however this would mean we'd have to
relabel the Hasse diagram at construction time rather than when calling
`hasse_diagram()`. This also has the drawback of not being able to use the
same digraph for all relabelings of a poset, which is probably used by the
linear extensions and creates a much larger memory usage (and data
duplication).
Hopefully before you have gotten angry, I think better standardization
could be used here too.
I'm also not quite sure #17051 is because of this behavior, but I haven't
really looked into it.
--
Ticket URL: <http://trac.sagemath.org/ticket/14019#comment:33>
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