#12587: simplicial complexes lack hash function
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Reporter: vpilaud | Owner: sage-combinat
Type: defect | Status: needs_review
Priority: major | Milestone: sage-5.4
Component: combinatorics | Resolution:
Keywords: | Work issues:
Report Upstream: N/A | Reviewers:
Authors: Travis Scrimshaw | Merged in:
Dependencies: | Stopgaps:
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Comment (by stumpc5):
Since you propose to make the hash only dependent on the facets:
{{{
sage: S = SimplicialComplex([1,2,3],[[1,2]])
sage: S
Simplicial complex with vertex set (1, 2, 3) and facets {(1, 2)}
}}}
({{{[1,2,3]}}} is actually not the vertex set, but the *ground set*, while
the vertex set is {{{[1,2]}}}.) The proposed implementation only takes the
facets into account for hashing, thus we get the same hash for
{{{
sage: S = SimplicialComplex([1,2],[[1,2]])
sage: S
Simplicial complex with vertex set (1, 2) and facets {(1, 2)}
}}}
Is this the desired behaviour - or should the ground set be used as well
for hashing?
(I don't have a strong opinion on this question, but I thought I bring it
up anyway. If you don't want to take care of the vertex set vs. ground set
issue in this ticket here, I will open another and ask for other peoples
opinion there.)
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/12587#comment:20>
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