#13222: Fix is_graded for Posets to use appropriate definition
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Reporter: aschilling | Owner: sage-combinat
Type: defect | Status: new
Priority: major | Milestone: sage-5.3
Component: combinatorics | Resolution:
Keywords: sd40 | Work issues:
Report Upstream: N/A | Reviewers: Anne Schilling, SD40
Authors: Franco Saliola | Merged in:
Dependencies: | Stopgaps:
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Description changed by nthiery:
Old description:
> Fix is_graded to use the following definition ``a poset is graded if
> all maximal chains have the same lengths``. See Stanley, EC1.
>
> As per this definition, the following poset is not graded:
>
> {{{
> sage: P = Poset([[1,2,3,4], [[1,2],[2,4],[3,4]]])
> sage: P.is_graded()
> True
> }}}
>
> Beware that not everybody agree on this choice of definition for
> ranked / graded. See http://en.wikipedia.org/wiki/Graded_poset.
>
> See also: #12993
New description:
Fix is_graded to use the following definition ``a poset is graded if
all maximal chains have the same lengths``. See Stanley, EC1.
As per this definition, the following poset is not graded:
{{{
sage: P = Poset([[1,2,3,4], [[1,2],[2,4],[3,4]]])
sage: P.is_graded()
True
}}}
See #13223 for a followup!
Beware that not everybody agree on this choice of definition for
ranked / graded. See http://en.wikipedia.org/wiki/Graded_poset.
See also: #12993
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Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/13222#comment:3>
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