#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):
Replying to [comment:22 jhpalmieri]:
> I think that the hash should only depend on the facets; the unused
vertices shouldn't have any effect. That makes the most mathematical sense
to me.
I agree.
But I still think that mathematically, a vertex is a 0-dimensional face,
and thus must be contained in some facet, see [1] or basically any book on
simplicial complexes. In the example above, {{{3}}} is therefore not a
vertex. (In particular, "unused vertices" do not exist.) But this is then
another issue, and we can discuss it on another ticket, as Travis
suggested as well.
[1] http://en.wikipedia.org/wiki/Abstract_simplicial_complex : "The vertex
set of Δ is defined as V(Δ) = ∪Δ, the union of all faces of Δ"
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Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/12587#comment:23>
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