In elementary geometry, a polytope is a geometric object with flat sides, and may exist in any general number of dimensions n as an n-dimensional polytope or n-polytope. (Def: http://en.m.wikipedia.org/wiki/Polytope)

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What are the least number of extremal points on a polytope?

Given a polytope $P$ embedded in $\mathbb{R}^D$. I can't prove the property that any facet of the polytope will have at least $D$ extremal points lying on it. I can see it for the case $D=2$ but not ...
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What is the equation of a facet and it's relation with all points of the polytope?

I was reading about polytopes and I came across about how to define equations of facets defining the polytope. The source I am reading from says If $n$ is a normal vector to a facet $F$ of a ...
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26 views

Characterize polytopes resulting from cutting a convex polytope by a hyperplane

We have a convex polytope $P$ for which we know its set of vertices. Using this set we characterize the H-representation of $P$ as: $\mathbf{A}\mathbf{x} < \mathbf{b}$. If a hyperplane defined by ...
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63 views

Intersection between a hyperplane and a convex polytope [on hold]

We work over $\mathbb{R}^N_+$, where $N \ge 2$. We are facing a situation in which we need to find the intersection between a hyperplane and a convex polytope. In detail, let $V$ be the set of ...
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polytope with 12 vertices and 48 edges

It seems like you can construct a polytope with 12 vertices, where each vertex connects to all the other vertices except 3. So there must be a totalt of 48 edges. (each of the 12 vertcies connects to ...
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32 views

Half space representation of a convex polytope

We know that the half space representation of a polytope is given by: $Ax<b$. Consider a convex polytope in $\mathbb{R}^3_+$ with vertices given by the following set of points: ...
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Volume of Convex Polytope with rational Entries

I have the following question: In this article Polytope volume computation it is stated that when considering a bounded convex polytope $P=\{x \mid Ax\le b\}$ with the matrix $A$ and the vector $b$ ...
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69 views

Find the intersection between two convex hulls, in this specific case

We work over $\mathbb{R}^K$. Let $V$ the set of vectors whose coordinates take values $0$ or $1$, or equivalently the corners of the unit cube $[0,1]^K$, . Let $d:\{0, \ldots, K\} \to \mathbb{R}_+$ ...
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103 views

How to determine whether a polytope is self-tessellating?

I'm looking for polytopes that can be tessellated by a finite number of scaled versions of themselves. I'll use the term component for such a scaled version in the text below. Self-tessellating ...
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Is this expression for the sub-dimensional volume of a convex polytope correct?

Let $\mathbf{S}$ be an $m\times n$ real matrix, with $m\le n$. Let $\vec{a}$, $\vec{b}$ be two real $n$-vectors, such that $a_i < b_i$ for all $i$. Consider the system of equations: ...
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Nice embedding of the permutohedron of order $n$ in ${\mathbb R}^{n-1}$

The permutohedron $P_n$ of order $n$ ($n\geqslant 2$) is the convex hull of the points $P_\pi=(\pi(1),\dots,\pi(n))$ where $\pi$ ranges over all permutations of $\{1,2,\dots,n\}$. Obviously, since ...
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Intersection numbers on blow ups of toric varieties

Suppose we have a smooth, complete toric varietiy $X_{\Sigma}$ of dimension $n$. Let $\sigma_k \in \Sigma(k)$ a smooth $k$-dimensional cone in $\Sigma$ and suppose we make the toric blow up at the ...
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38 views

From a set of vertices, find smallest polytope enclosing another point

Out of a set of vertices $V=\{\vec v_i\in \mathbb R^D\}$, I am constructing a piecewise linear interpolating function $f:\mathbf{conv}(V)\rightarrow R$ as follows: given a point $\vec d\in ...
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26 views

How to find the center of mass (not vertex average) of a convex hull?

I have found results that say that computing the average of vertices of a polytope presented by inequalities is a #$P$-hard problem. However what if we want the true center of mass (determined by ...
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What is the definition of a polytope in terms of set theory?

I know that the set definition of a polytope $P^+_f$ associated with a polymatroid function f is: $$ P^+_f = \{ y \in \mathbb{R}^V_+ : y(A) \leq f(A), \forall A \subseteq V\}$$ where $y(A) = \sum_{i ...
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63 views

Uniform lattice sample inside a particular convex polytope

[update]: hardmath suggests using tools from linear programming. This looks like a good idea indeed. I can now tell that my feasible set is described by: $Set = \{d \in \mathbb{N}^c, -B.d\leqslant ...
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How to generate a ploytope with a finite number of simplices

Well to solve this problem I wanted to show that a polytope with r- lineraly independent vertices is the finite union of r-simplices, but I am stuck in that because I dont know how to proceed and ...
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37 views

The number of vertices in a polytope is finite [duplicate]

I want to prove the following: Let $K$ be a convex polytope. Show that $K$ has a finite number of extreme points. I have seen the bound for the cardinality of the set of extreme points: $|E| \leq ...
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32 views

Prove that a convex polytope has a finite number of extreme points

I want to solve this problem: Let $K$ a convex polytope.Show that $K$ has a finite number of extreme points. My attempt: Is clear that the extreme points of a polytope are the vertices, now, these ...
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3D models of the unfoldings of the hypercube?

There are (apparently) 261 distinct unfoldings of the 4D hypercube, a.k.a., the tesseract, into 3D.1 These unfoldings (or "nets") are analogous to the 11 unfoldings of the 3D cube into the plane.2 ...
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Does a totally normalized version of a sub modular function form the same polymatroid?

Consider any sub modular function $f$: $$f(A) + f(B) \geq f(A \cup B) + f(A \cap B)$$ and a totally normalized version of f $\bar{f}(A) = f(A) - m(A)$ where $m(A)$ is a modular. Consider the ...
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How many top-$k$ orderings can be induced by linear functionals on integer points in a square?

Let $X = ([1,n] \times [1,n]) \cap {\mathbb N}\times {\mathbb N}$ for positive integer $n$. For $k \leq n^2,$ a top-$k$ ordering $(x_{a_1},x_{a_2}, \ldots, x_{a_k})$ induced by a vector $c$ is a ...
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Exposed point of a compact convex set

I'm trying to show that given a compact convex set $K$ in $R^d$, there must be at least one exposed point (where $v$ is exposed if there exists a hyperplane H such that $H \cap K = \{v\}$ . This is a ...
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28 views

Vertex Figure of Leech Lattice

I'm doing some research on the newton number (kissing #) problem and it would be extremely useful to know the type and number of elements, particularly the facets, of the vertex figure formed from the ...
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Is there any study on noncrossing partitions for cyclic polytopes?

I am from another area of maths, and has never learnt combinatorics and polytope theory properly before, so please feel free to point out any mistake/misuse of terminology. The starting point is the ...
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51 views

Sparse & Dense Polynomials

I've been reading up on Bernstein's theorem for an algebraic geometry assignment and I've come across the terms "dense" and "sparse" in relation to the polynomials. However, I have been unable to find ...
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Edges of a permutohedron

Consider a permutohedron $P_n$ (this is a polytope which is a convex hull of $n!$ points, which are obtained from $(1,2,...,n)$ by all possible permutations of coordinates). I have to prove the ...
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Hamilton Path Polytope

How can someone prove that the $\{dim(H)=\frac{n(n-1)}{2} uncorrect\ see\ update\}$ where $H$ is the Hamilton path polytope of a complete graph $K_n$, that consists of vertices $x\in\{0,1\}^{\mid ...
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Uniform Sampling over Convex Polytope (not full-dimensional)

I want to simulate a uniform distribution on a convex polytope that is not full-dimensional for optimization purposes (to generate random points on the set I want to minimize over). The polytope is ...
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What are higher degree cantellations?

Compare higher degree rectifications. What are higher degree cantellations? I didn't find any definition on internet, at least no operational description. You can find constructions by ...
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Prove that a convex $d$-polytope has at least $d+1$ facets

This seems trivial but I can't come up with a formal proof. I think there should be a way to do this inductively but I can't figure out how$\ldots$ Any help much appreciated
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The number of $(d-1)$-faces in a $d$-polytope is at least $(d+1)$

I have to try to prove the following: Let $V = {v_1,...,v_n} \subset \mathbb{R}^d$ be a point configuration affinely spanning $\mathbb{R}$ (i.e., $\operatorname{aff}(V) = \mathbb{R}^d)$. Let $H$ be ...
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Number of Half-Unit Pentachora in a Unit Hexacosichoron

As the title summarizes, I am unable to find out how many 5-cells {3,3,3} (pentachora) with a circumscribed diameter (d) of 1/2 can fit into a 600-cell {3,3,5} (hexacosichoron) with d=1, {3,3,3,6}. ...
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How to show that the vertices of a convex hull are given by these specific subsets…

We work over $\mathbb{R}^N$. Let $V$ be the corners of the unit cube $[0,1]^N$, or equivalently the set of vectors whose coordinates take values $0$ or $1$. Let $d:\{0, \ldots, N\} \to \mathbb{R}_+$ ...
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Proof: Minkowski sum polytope implies A and B polytopes

Suppose $A$ and $B$ are convex sets and their Minkowski sum $A+B$ is a polytope. How do you prove that $A$ and $B$ are polytopes as well?
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On the Name of the Amplituhedron

Shouldn't the 'amplituhedron' really be called an 'amplitutope' since it's really a polytope and not strictly a polyhedron?
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Count and description of vertices of certain faces of the Tridiagonal Birkhoff polytope $\Omega^t_{d+k}$

For $k \ge 1$, $d \ge 2$ and $k \le d - 1$, let ${}^f_d\Omega^t_{d+k} (d;c_k(d - 1))$ be the intersection of $k - 1$ facets of the Tridiagonal Birkhoff polytope $\Omega^t_{d+k}$ with equations: ...
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dimension of Weber set and selectope (as a operator)

Let $\Omega$ be a finite set of players. For a selector $\alpha:(2^{\Omega}-\{\emptyset\})\rightarrow\Omega$, we define a marginal value operator as a linear operator $m^{\alpha}$ ...
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Extra information needed to distinguish combinatorially isomorphic polytopes

The title pretty much sums up my question: what extra information do we need (or what is an example of sufficient information) on top of the face lattice in order to completely characterize a convex ...
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34 views

Discrete Analogue of the Poincaré Conjecture and Simple Connectedness

I apologize if this question is badly worded or obvious, but I have no formal topology background. I have put some effort into trying to find something, but nothing turned up, perhaps due to my lack ...
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linear algebra question

Consider $n$ convex polytopes $S_1, \cdots, S_n$ and a set of matrices $W$ such that each matrix $A\in W$, we have that the $i$-th row of $A$ is a member of $S_i$. (In general $W$ is infinite.) ...
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What are the facets of the Tridiagonal Birkhoff $d$-polytope $\Omega^t_{d+1}$?

The Birkhoff $d$-polytope $\Omega_{d+1}$ is the convex polytope in $\mathbb{R}^{d+1}$ $\times$ $\mathbb{R}^{d+1}$ of doubly stochastic matrices: • All matrices contained in $\Omega_{d+1}$ have ...
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Projection onto hypercube [0,1]^n

Given a positive n-dimensional vector $\mathbf{z}$ (all its elements are positive), my goal is to project it to a unit hyperplane $[0,1]^n$. However my projection is defined with respect to ...
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Ehrhart polynomial of lattice tetrahedrons in $\Bbb{R}^4$

Let $\lbrace v_1 , v_2, v_3 , v_4 \rbrace \subset \Bbb{Z}^4$ be linearly independent, and denote by $P$ the convex hull of this set. Now, $P$ is a 3-polytope residing in four-dimensional space. What's ...
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Faces of the Permutahedron

We define the Permutahedron as the convex hull of all permutations of the vector $(1,2,\dots,n)\in\mathbb R^n$. I am having trouble seeing why the number of $n-k$ dimensional faces of this polytope is ...
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131 views

Why is the 24-cell (also called Icositetrachoron or Hyperdiamond) the unique regular convex polychoron which has no direct three-dimensional analog?

The 24-cell is self-dual, and is the unique regular convex polychoron which has no direct three-dimensional analog. http://mathworld.wolfram.com/24-Cell.html I don't understand why that is ...
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If we inscribed all the 6 regular convex four-dimensional polytopes in a sphere, which one would have the highest volume?

When a dodecahedron is inscribed in a sphere, it occupies more of the sphere's volume (66.49%) than an icosahedron inscribed in the same sphere (60.54%). But what about for the 6 regular convex ...
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What are the formulas for the number of vertices, edges, faces, cells, 4-faces, …, $n$-faces, of convex regular polytopes in $n \geq 5$ dimensions?

I know that in dimension $n \geq 5$ there are only 3 kind of convex regular polytopes in each dimension: the $n$-simplex, the $n$-cube and the $n$-orthoplex. I would like to know if there are ...
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36 views

Number of 3-way contingency tables

Denote by $f(n)$ the number of $2\times 2 \times 2$ contingency tables with all 2-dim marginals equal to $n$. What is $f(n)$? It is easy to see that $f(n)$ is polynomial of degree 4, since it ...
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Volume of a polytope with relaxed constraints

Consider a polytope in $n$ dimensions defined by a set of linear constraints: $$P = \{x \in \mathbb{R}^n : Ax \leq b\}$$ where A is some $m \times n$ constraint matrix, and $b = (b_1,\ldots,b_m)$ is ...