#12993: Bug in determining whether a poset is graded
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Reporter: saliola | Owner: sage-combinat
Type: defect | Status: new
Priority: major | Milestone: sage-5.1
Component: combinatorics | Keywords: poset, combinat
Work issues: | Report Upstream: N/A
Reviewers: | Authors:
Merged in: | Dependencies:
Stopgaps: |
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This should return True:
{{{
sage: P = Poset(([1,2,3,4],[[1,4],[2,3],[3,4]]), facade = True)
sage: P.is_graded()
False
}}}
Anne's suggestion from this [https://groups.google.com/d/topic/sage-
combinat-devel/XsMrxKdvl1A/discussion thread] on sage-combinat-devel:
For a finite poset perhaps the easiest would be to
- start with a random element in the poset, assign rank 0
- look at all covers and cocovers and assign the rank according to the
recurrence rank(x) = rank(y) + 1 if x covers y.
- repeat with the new elements
- if at any point an element is reached again and is assigned a
different value from before, the poset is not graded; otherwise continue
with new elements
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/12993>
Sage <http://www.sagemath.org>
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