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Finite or discrete collections of geometric objects. Packings, tilings, polyhedra, polytopes, intersection, arrangements, rigidity.

6 votes
Accepted

Regularity of Delaunay triangulation of a hypercube

"Finally my question is: how to triangulate a hypercube resembling (B)?" This is easy to do, and is normally called the "standard triangulation" of the $n$-cube. Consider all the monotone edge paths …
Francisco Santos's user avatar
13 votes
Accepted

Does the Hirsch conjecture hold for $n < 2d$?

The answer is no, as follows from the following Lemma of Klee and Walkup: Lemma: If P is a d-polytope with n facets and we perform a "wedge" over any facet F we get a (d+1)-polytope P' with n+1 facet …
Francisco Santos's user avatar
3 votes

Average vertex degree in finite Delaunay triangulations in high dimensions

Let me point out a very significant difference between dimensions 2 and 3. In dimension 2 ANY triangulation (Delaunay or not, random or not) has average degree strictly smaller than six (and going to …
Francisco Santos's user avatar
3 votes

Vertex-transitive polytopes in any dimension with any number of vertices?

Gale transforms allow to settle the case of odd $d$ and even $v$ completely, in the positive (Matteo's answer in this case needed $v\ge 2d$). Remember that the Gale transform of a $d$-polytope with $v …
Francisco Santos's user avatar
7 votes
Accepted

Integer decomposition of dilated integral polytopes

The answer is YES in the following stronger form: Lemma 1: Let $d>n$ and let $p\in dP\cap \mathbb{Z}^n$. Then there is an $i\in\{1,\dots, n\}$ and points $p'\in iP\cap \mathbb{Z}^n$, $p_1,\dots, p_{d …
Francisco Santos's user avatar
38 votes
Accepted

Does every polyomino tile R^n for some n?

A positive answer to this question has just appeared in the arXiv: Tiling with arbitrary tiles; Vytautas Gruslys, Imre Leader, Ta Sheng Tan; http://arxiv.org/abs/1505.03697
Francisco Santos's user avatar
4 votes

A rational polytope that is not a 01-polytope?

Every simplicial polytope is rational, hence there are infinitely many rational polytopes in any fixed dimension. In contrast, there are finitely many 0/1 polytopes, since they cannot have more than $ …
Francisco Santos's user avatar
2 votes

n-dimensional Delaunay Triangulation of Lattices

The answer to 2 and 1 is "No". For (2), observe that a positive answer here would imply all Delaunay simplices to be unimodular (i.e., have volume equal to $1/n!$ times the volume of a fundamental p …
Francisco Santos's user avatar
5 votes

Which (semi)regular polyhedra are combinations of two others?

I think the whole list of Gjiergji (and lightly more, see below) follows from Wythoffian operations. For the cube-octahedron family, for example, consider the following diagram: The polyhedron along a …
Francisco Santos's user avatar