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Is it possible to compute the face lattice of a polytope from its vertex-facet incidences?

asked 2016-11-15 18:13:31 -0500

guillermo gravatar image

HI there,

I wonder if within sage it is possible to compute the face lattice of a polytope from its vertex-facet incidences. There is a known algorithm by Kaibel and Pfetsch (see, and we wonder if it has already been implemented in Sage.

Thanks, and regards, Guillermo

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answered 2016-11-16 01:42:19 -0500

slelievre gravatar image

updated 2016-11-16 01:42:35 -0500

By searching the documentation or the source files of Sage, you can get an answer.

Searching doc:

sage: search_doc('Kaibel')
html/en/reference/geometry/sage/geometry/polyhedron/base.html:1166:<tr><td class="label"><a class="fn-backref" href="#id1">[KP2002]</a></td><td>Volker Kaibel and Marc E. Pfetsch, &#8220;Computing the Face

Searching source:

sage: search_src('Kaibel')
geometry/polyhedron/            Volker Kaibel and Marc E. Pfetsch, "Computing the Face

Online documentation (append the result of "search_doc" to "").

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Hi slelievre,

Thank you for your reply. Sage computes the face lattice of a polytope using Kaibel and Pfetsch's algorithm. So a polytope must be given. However, for you to construct a polytope in Sage you need either vertex coordinates or hyperplane equations; that is, you need a geometric realisation of the polytope.

Vertex-facet incidences is a combinatorial object which doesn't know about a geometric realisation. For instance, the following gives the vertex-facet incidences of the Egyptian pyramid [[4,3,2,1],[4,3,0],[4,2,0],[3,1,0],[2,1,0]], where the [4, 3, 2, 1] are the vertices of one facet.

guillermo gravatar imageguillermo ( 2016-11-16 01:58:04 -0500 )edit

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Asked: 2016-11-15 18:13:31 -0500

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Last updated: Nov 16 '16