All Questions
Tagged with co.combinatorics triangulations
23 questions
0
votes
0
answers
98
views
Number of tetrahedra inside a sphere with boundary A
I understand, that there are some combinatorial problems which are not yet solved regarding gluing triangulations in 3D. At least last time I checked, it was not yet known exactly how many ...
- 183
9
votes
0
answers
212
views
Left adjoint functor between categories of polygons?
EDIT: Based on very helpful comments from Alec Rhea and Qiaochu Yuan I am adding some specification on objects and morphisms, hoping that this clarifies the idea behind these categories. I have also ...
- 6,937
8
votes
2
answers
850
views
Three-dimensional triangulations with fixed number of vertices
My question is the following:
Are there triangulations of $S^3$ which (a) are non-degenerate, (b)
have four vertices, and (c) have no edges of degree two?
A side question:
If one represents this ...
- 183
8
votes
3
answers
921
views
Alternating Sum Involving Catalan Numbers
I was wondering if anyone knew how to obtain a simpler closed form of the following sum(or had any other insights regarding it):
$$\sum_{k=0}^n (-1)^k{n \choose k} C_{2n-2-k} $$
Here $C_n = \frac{1}{n+...
- 509
9
votes
1
answer
793
views
Properties a triangulation must have in order to describe a manifold
I am mainly interested in the $3$-dimensional case. It is a well-known fact, following from the work of E. E. Moise and R. H. Bing in the 1950s, that every $3$-dimensional topological manifold (with ...
- 1,429
1
vote
0
answers
84
views
Number of polyhedral covers of a triangulation of $S^2$
For a given triangulation (combinatorial Type I. or Type II.) of a $2$-sphere, what is the number of unique polygonal covers with $n$ polygons where ($n$ goes from $2$ to $N$)?
Under polygonal cover, ...
- 183
0
votes
0
answers
125
views
Naming convention for different type of triangulations
When studying random geometries and related mathematical/physical stuff conflicting naming convention pops up regarding the naming of the different ensemble types of triangulations (in general ...
- 183
3
votes
0
answers
93
views
Minimal set of geometric moves in various equivalence classes of triangulated geometries
I would like to get to know what is the minimal set of geometric changes "aka. moves" (topology preserving modifications / Pachner moves / bistellar moves) that can transform any 3-...
- 183
8
votes
1
answer
618
views
When is a triangulation of sphere two-colorable?
Let $T$ be a triangulation of sphere. We say that $T$ is $k$-colorable if the triangles of $T$ can be assigned with $k$ colors such that any two triangles with a common edge have different colors.
I ...
- 30.6k
4
votes
1
answer
255
views
Is every (not necessarily PL-) triangulation of a manifold pure, non-branching and strongly-connected?
A triangulation of a topological manifold $\mathcal{M}$ possibly with boundary is an abstract simplicial complex $\Delta$ together with a homeomorphism $\varphi:\vert\Delta\vert\to\mathcal{M}$, where $...
- 1,171
12
votes
0
answers
229
views
3-manifolds with stacked links
Stacked spheres
A triangulation of a 2-dimensional sphere is called a stacked sphere if it is obtained inductively from the boundary of a 3-simplex by deleting a 2-face (triangle) $T$ adding a new ...
- 24.7k
6
votes
2
answers
159
views
Eberhard-type theorems for Fisk triangulations?
A triangulation of a surface is called a Fisk triangulation if the degree of all but two vertices is even, and these two exceptional vertices of odd degree are neighbors.
I would like to know what ...
- 19.1k
12
votes
4
answers
2k
views
What is the number of equitriangulations of the n-cube?
I wonder if this question has been considered before and if anything is known. My search attempts have failed so far.
Let's consider the n-dimesnional cube, $[0,1]^n$, and let's call a simplex with ...
- 85.6k
29
votes
1
answer
2k
views
High-Dimensional Analogs of Polygon Spaces
[Edit: I had a mistake in the numerology (took d=6,5 instead of d=5,4). Edit: I mistakenly identified my mistake, it is 6,5 but I got the indices shifted by one.]
Background: Polygon spaces
Given a ...
- 24.7k
2
votes
0
answers
87
views
Existence of a "generic enough" lattice point interior to a lattice triangle
Let $T$ be a lattice triangle in $\Bbb R^2$ (i.e. the convex hull of three noncolinear points in $\Bbb Z^2$), and assume it has at least one interior lattice point. Is it always possible to find a ...
- 3,079
4
votes
0
answers
286
views
Mean number of $n$-simplices per $(n-2)$-simplex in a triangulated $n$-manifold
Work by Tamura (extending results by Luo and Stong) shows the following.
Theorem: For any closed 3-manifold $M$ and any rational number $4.5 < r < 6$ there is a triangulation $T$ of $M$ for ...
- 175
4
votes
1
answer
172
views
The number of simplicial and general $d$-polytopes with $d+3$ labelled vertices
Micha Perles used Gale diagrams to compute the number of simplicial $d$-polytopes with $d+3$ vertices and of general $d$-polytopes with $d+3$ vertices. The computation can be found in Chapter 6.3 of ...
- 24.7k
5
votes
1
answer
261
views
Do random triangulation edge-flips maintain randomness?
Let $S$ be a fixed set of $n$ points in the plane in general position.
Let $T$ be a triangulation
of $S$, (somehow) selected
uniformly at random from all triangulations of $S$.
(There are an ...
- 151k
9
votes
1
answer
424
views
Hamiltonian circuit
Let us consider a disk with one labelled point on the boundary and $n$ labelled points in the interior.
Let T be a triangulation of the whole disk with vertices on the labelled points such that T ...
- 828
3
votes
0
answers
387
views
regular triangulations of the product of two simplices
Is description of all regular triangluations of $\Delta^n\times \Delta^k$ known? (Regular triangulations are those which correspond to vertices of Gelfand--Kapranov--Zelevinsky secondary polytope, or, ...
- 109k
3
votes
1
answer
445
views
Dehn-Sommerville relations for $\Delta$-complexes
Let $M$ be a closed, triangulated manifold of dimension $m$ and $K(M)$ be its triangulation. Let $f_i$ denote the number of $i$-simplices of $K(M)$. As proved by Klee the face numbers satisfy the ...
- 1,017
7
votes
1
answer
186
views
How many maximal triangulations of a rectangle?
I posted the following question on MathStackExchange, but I didn't any answer. So please let me post it on MathOverflow.
Let $L_{m,n}\subset\mathbb R^2$ be a rectangle given by $[0,m]×[0,n]$ with $m,...
- 71
1
vote
0
answers
247
views
dissections and vertices of non-convex polytopes
Let us call a finite union $P$ of $n$-dimensional compact convex polytopes in $\mathbb{R}^n$ a non-convex polytope. Recall that a dissection of $P$ is a finite collection $T$ of $n$-dimensional ...
- 14k