#14019: equality is broken for Posets
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Reporter: ncohen | Owner: sage-combinat
Type: defect | Status: new
Priority: major | Milestone: sage-5.7
Component: combinatorics | Keywords:
Work issues: | Report Upstream: N/A
Reviewers: | Authors: Nathann Cohen
Merged in: | Dependencies:
Stopgaps: |
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Plain and simple :
{{{
sage: d = DiGraph({2:[1],3:[1]})
sage: p1 = Poset(d, linear_extension = [1,2,3])
sage: p2 = p1.relabel({1:1,2:3,3:2})
sage: p1.hasse_diagram() == p1.hasse_diagram()
True
sage: p1 == p2
False
}}}
This can be fixed by saying that two posets are equal if their hasse
diagrams are equal, as it should have been since the beginning.
This will probably make poset equality much slower. On the bright side it
will work correctly.
Of course this patch could have been almost trivial, but there is in the
FinitePoset class a "key" argument, whose purpose is to make two posets
different if they have different keys. So this patch checks that too.
And the next time that somebody will need to store pairs "(a poset, a
key)", the best will be to store pairs "(a poset, a key)". And not "A
poset with a key included inside, which is useful just for my own code" as
one could easily believe.
Oh. And the same with linear orderings, of course.
Nathann
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/14019>
Sage <http://www.sagemath.org>
Sage: Creating a Viable Open Source Alternative to Magma, Maple, Mathematica,
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