Skeleton
The k -skeleton of a polytope is the set of all elements of with rank at most equal to k .[1]
The 1 -skeleton of a polytope can be thought of as a graph with its vertex set being the vertices of the polytope and its edge set being the edges of the polytope.[1] Thus two vertices are adjacent iff there is an edge in the polytope which is incident on both of them. This graph may be referenced by a number of names. Since the 1 -skeleton is the most commonly used k -skeleton it may be referred to as "the skeleton" of a polytope without a qualifying numeral. It may also be called simply the graph of a polytope or the vertex adjacency graph of a polytope.
Properties[edit | edit source]
All vertices of the 1-skeleton of a Euclidean polytope of rank d have a degree of at least d . This is not necessarily true of abstract polytopes, maniplexes or polytopes in other spaces.
Polytopes of different ranks can have the same 1-skeleton. The complete graph is the 1-skeleton of both a 4-polytope and 5-polytope.
A finite graph is the 1 -skeleton of a finite convex polyhedron iff the graph is 3-vertex-connected and planar.[2][3] Such graphs are called polyhedral graphs.
References[edit | edit source]
- ↑ 1.0 1.1 Kalai (2017:505)
- ↑ Kalai (2017:506)
- ↑ Steinitz (1922:22)
Bibligraphy[edit | edit source]
- Kalai, Gil (10 August 2017). "Polytope Skeletons and Paths" (PDF).
- Steinitz, Ernst (1922). "Polyeder und Raumeinteilungen" [Polyhedra and Divisions of Space]. Encyclopädie der mathematischen Wissenschaften, Band 3 (Geometries) [Encyclopedia of the Mathematical Sciences, Volume 3 (Geometry)] (in German).