#14019: equality is broken for Posets
-------------------------------------+-------------------------------------
Reporter: ncohen | Owner: sage-combinat
Type: defect | Status: needs_work
Priority: major | Milestone: sage-6.4
Component: combinatorics | Resolution:
Keywords: posets | Merged in:
Authors: Travis Scrimshaw, | Reviewers: Travis Scrimshaw,
Anne Schilling | Anne Schilling
Report Upstream: N/A | Work issues:
Branch: | Commit:
public/combinat/poset/fix_equality-14019|
68c2902122a52cc16a13831b80d7a52c4e98fe86
Dependencies: #17059 | Stopgaps: #14185
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Comment (by ncohen):
Hello !
I think that there is something wrong with the code for canonical label:
{{{
sage: Poset(digraphs.Path(10)).canonical_label().linear_extension()
[0, 9, 7, 5, 3, 2, 4, 6, 8, 1]
}}}
In particular, the code looks like you suppose that `range(n)` is a linear
extension of a canonically labelled digraph, and this is wrong:
{{{
sage: digraphs.Path(10).canonical_label(certify=True)[1]
{0: 0, 1: 9, 2: 7, 3: 5, 4: 3, 5: 2, 6: 4, 7: 6, 8: 8, 9: 1}
}}}
This seems to work fine with the latest beta release
{{{
sage: Poset(digraphs.Path(10)).canonical_label().linear_extension()
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
}}}
Nathann
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Ticket URL: <http://trac.sagemath.org/ticket/14019#comment:58>
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