**11**

votes

**2**answers

2k views

### Subdivision of triangles into congruent triangles

Recently some old notes of mine have gotten me to thinking about the problem of subdividing a triangle into $N$ smaller triangles, all congruent to one another. A little thought shows the following ...

**0**

votes

**0**answers

55 views

### Convergence of Discrete Geodesic

Let $M$ be a Riemmanian manifold, $p\in M$ and $V\in T_p(M)$.
Suppose $f^{-1}:U_p \mapsto U$ is a diffeomorphism of a neighborhood of p to an open subset of $\mathbb{R}$ and define the sequence:
\...

**1**

vote

**0**answers

40 views

### Transformation inverting distances between two sets of diameter 1

Let $S_1, S_2 \subseteq \mathbb{R}^2$ be two disjoint sets of points in the plane with $\texttt{diam}(S_1) \leq 1$ and $\texttt{diam}(S_1) \leq 1$.
Does there always exist a transformation $f: S_1 \...

**15**

votes

**1**answer

610 views

### On convergence of convex bodies

Let $K\subset \mathbb{R}^n$ be a compact convex set of full dimension. Assume that $0\in \partial K$.
Question 1. Is it true that there exists $\varepsilon_0>0$ such that for any $0<\...

**0**

votes

**0**answers

55 views

### Number of polyhedra with N faces?

A. Up to isomorphism, how many polyhedra with N faces are there? Assume each face can be a triangle, square, pentagon, hexagon, etc... Furthermore each edge can be resized to any nonzero positive ...

**7**

votes

**1**answer

258 views

### Set of balls which the number of the ball intersects lines on the plane is bounded

Does there exist the set of balls(may be not disjoint) $X=\{B_i\subset\mathbb{R^2};i\in I\}$, satisfing following properties?(Note that the ball has a positive real radius)
Let the set of all lines ...

**13**

votes

**2**answers

577 views

### Lattice n-gons with ordered side lengths 1,2,3,…,n

Consider the octagon in the Cartesian plane with vertices at (0,0), (1,0), (1,2), (4,2), (4,6), (7,2), (7,8), and (0,8).
Are there other (infinitely many) polygons, such as this, lying entirely in ...

**9**

votes

**2**answers

465 views

### Dissecting Ramanujan´s Cuboid: 1729 = 19 x 13 x 7

Consider the cuboid of dimensions 19 x 13 x 7 whose volume is 1729, the Hardy-Ramanujan number. What is the least number of smaller cuboids into which it can be dissected so that the resulting pieces ...

**22**

votes

**4**answers

1k views

### Visibility of vertices in polyhedra

Suppose $P$ is a closed polyhedron in space (i.e. a union of polygons which is homeomorphic to $S^2$) and $X$ is an interior point of $P$. Is it true that $X$ can see at least one vertex of $P$? More ...

**8**

votes

**0**answers

116 views

### Computer searches for the $g$-conjecture

McMullen's $g$-conjecture aims the classify possible $f$-vectors of simplicial $d$-spheres. The $g$-conjecture has been proven for polytopal spheres and for simplicial spheres of dimension $d < 5$. ...

**3**

votes

**0**answers

42 views

### Connectedness of semi algebraic set by c.a.d

I do not know whether there is a standard or some traditional ways to decide whether a semi algebraic set is connected or not.
One way I know is c.a.d algorithm. I have read some papers of c.a.d ...

**6**

votes

**2**answers

193 views

### Graphs with prescribed numbers of k-cliques

Let $(a_1,a_2,\dots, a_n)$ be a sequence of non-negative integers.
Q. When does there exists a simple graph $G$ such that its number of $k$-cliques is $a_k$ (that is $G$ has $a_1$ vertices, $a_2$ ...

**2**

votes

**1**answer

86 views

### How many distinct sets of n collinear points are there in an evenly-spaced two-dimensional grid of m x m points?

I'm seeking the definition of some function $f(n,m)$ which evaluates to the number of distinct sets of $n$ collinear points which are selected from an evenly-spaced two-dimensional grid of $m \times m$...

**2**

votes

**1**answer

127 views

### How many lines of exactly n points can be placed in a discrete, square grid of size m x m?

Per the title, I'm seeking the definition of a function $f(n, m)$ which evaluates to the number of lines made from exactly $n$ points which can be placed on a two-dimensional discrete, square grid of ...

**2**

votes

**0**answers

45 views

### lower bound for sum of (squared) distances under a minimum distance restriction

I am trying to solve a packing problem in discrete geometry and it would be useful to know the answer to the following problem.
Let $A_1$, $A_2$,..., $A_n$ be $n$ points in the Euclidean plane $\...

**30**

votes

**3**answers

2k views

### Can one recover the smooth Gauss Bonnet theorem from the combinatorial Gauss Bonnet theorem as an appropriate limit?

First let me state two known theorems.
Theorem 1 (for smooth manifolds): Let $(M,g)$ be a smooth compact two dimensional Riemannian manifold. Then
$$ \int \frac{K}{2 \pi} dA = \chi (M) $$
where $K$ ...

**0**

votes

**0**answers

33 views

### Experimental Investigations on the Statistics of Infinite, Discrete, Evenly Distributed Pointsets in the Euclidean Plane

I am trying to estimate the distribution of certain planar polygons in the Euclidean plane; to accomplish that, I generate finite set of points, that are evenly distributed in w.l.o.g. the $[0,1)\...

**3**

votes

**2**answers

105 views

### Unit-Distance Polyhedra

What polyhedra are known to have two vertices adjacent if and only if they are of distance $d$ apart, for fixed $d$? For example, regular Platonic solids satisfy this condition, so I am looking for ...

**21**

votes

**2**answers

2k views

### Is it possible to dissect a disk into congruent pieces, so that a neighborhood of the origin is contained within a single piece?

Problem: is it possible to dissect the interior of a circle into a finite number of congruent pieces (mirror images are fine) such that some neighbourhood of the origin is contained in just one of the ...

**14**

votes

**1**answer

350 views

### Banach-Mazur distance between the cube and the octahedron

The Banach-Mazur distance $d(X, Y)$ between two normed spaces $X, Y$ of the same dimension is defined as $d(X, Y) = \log\inf \|T\| \cdot \|T^{-1}\|$, where the $T:X \to Y$ is a linear and invertible ...

**4**

votes

**0**answers

54 views

### Efficient CW structures on squarefree semi-algebraic set

General Setup
Given a collection of $k$ polynomials (with real coefficients) in $n$ real variables, say $f_i(x_1,\ldots,x_n)$, let $V \subset \mathbb{R}^n$ correspond to those $x$-values for which ...

**5**

votes

**1**answer

125 views

### Decidability of convex rearrangements of polygons

Triggered by the MO question,
"How many convex shapes can be made with the pieces of the Stomachion?," I would like to pose this question:
Q. Given $n$ polygons in a set $S$, say each with integer ...

**4**

votes

**2**answers

131 views

### Classification of symmetries of tilings in surfaces?

Is there a general study of the symmetries of tilings on surfaces?
Conway, Goodman-Strauss & Burgiel classified them on $\mathbb S^2, \mathbb R^2$ and $\mathbb H^2$, with their 'Magic Theorem'. ...

**7**

votes

**1**answer

69 views

### minimum number of bases of a matroid, that comes from a convex polytope

Given a d-dimensional polytope P with n points, then what is the minimum number of simplices that are spanned by vertices of P? This question led my research to matroids and so my question is: what is ...

**3**

votes

**0**answers

107 views

### Zeros of Hilbert series of affine toric varieties

Consider a convex rational polyhedral cone $C\subset\mathbb R^m$ with vertex at the origin. Let $X$ be the corresponding affine toric variety, i.e. $\mathbb C[X]=\mathbb C[\mathbb Z^m\cap C^\circ]$. ...

**4**

votes

**2**answers

222 views

### (non-)existence of the aperiodic monotile

The aperiodic monotile problem asks whether there exists a single tile that every tiling of the plane made with it results non-periodic. What is known about this problem? If this tile exists, how can ...

**2**

votes

**0**answers

53 views

### What do you call the collection of all sets shattered by $F$?

The proof of Pajor's lemma uses the collection of all sets $S\subseteq X$ shattered by some $F\subseteq 2^X$. Is there a standard term for the former object? I've been privately referring to it as the ...

**7**

votes

**1**answer

151 views

### Penrose tiling substitution is bijective

Let $\mathcal{P}$ a Penrose tiling built by a substitution $\omega$ with two triangles.
It is claimed, for instance, in the article of Anderson and Putnam "Topological invariants for substitution ...

**0**

votes

**0**answers

34 views

### Minimal subset of an $n$-dimensional grid intersecting every ($n$-dim) arithmetic progression of length $k$

Let $$A=\{1,2,...,l\}^n \subset \mathbb{R}^n$$ for some positive integers $l$ and $n$, and $B \subset A$ be a set such that $|B| \ll l^n$. I am interested in determining how small must $B$ be in ...

**14**

votes

**0**answers

152 views

### Precise estimate for probability an $n$-point set has diameter smaller than $1$

This question was inspired by an earlier question that I answered but would like a more precise bound for.
Consider random points $x_1, \dots, x_n$ in the unit ball in $\mathbb R^d$, uniformly and ...

**2**

votes

**0**answers

85 views

### Balanced partitions of vector sets

We are interested in the following
Lemma. Let $V\subset [0,1]^n\subset\mathbb R^n$ be a set of $n$-dimensional vectors. Then for each $r\le |V|$ there exists a partition $$V=V_1\cup V_2\cup\dots \cup ...

**1**

vote

**1**answer

72 views

### Testing whether two vertices are neighbours

I face the following problem: I am given a high-dimensional, convex, bounded polyhedron in both vertex description: $X = \mathrm{conv} \, \{ v_1, \ldots, v_K \}$ and halfspace description: $X = \{ x \...

**5**

votes

**2**answers

143 views

### Minimum length of a convex lattice polygon containing k lattice points?

Let $f(k)$ denote the minimum length of a convex lattice polygon containing exactly $k$ lattice points (including lattice points on the boundary).
It is not too hard to show that $k = \frac{1}{4\pi} ...

**1**

vote

**1**answer

162 views

### Constant hole density on the area of a circle

I need to create about 100 (small) holes in a distributor plate (hole diam = 0.5 mm; plate diameter = 100 mm). The sm. holes should be distributed in such a way that the density (hole/area) is nearly ...

**8**

votes

**0**answers

454 views

### Maximal set on hypersphere that does not contain pairs of orthogonal vectors

Let R be a region on a hypersphere. Each point A of the hypersphere
is associated with a vector pointing to A and with origin at
the centre of the hypersphere. So let me identify each point with a
...

**3**

votes

**0**answers

272 views

### Generalization of the “double cap conjecture” to a vector space with complex field

The conjecture that I proposed in
Maximal set on hypersphere that does not contain pairs of orthogonal vectors
is in fact known as the "double cap conjecture", as noted by Guillaume Aubrun.
See for ...

**3**

votes

**1**answer

300 views

### Radial tilings with variable area ratios

I was looking at this neat page on logarithmic spiral tilings when a question popped up:
http://www.uwgb.edu/dutchs/symmetry/log-spir.htm
It seems that in all of the tilings shown, the area of each ...

**3**

votes

**0**answers

164 views

### An isoperimetric inequality for “order” polytopes

I am looking for an isoperimetric inequality for order-like polytopes.
An order polytope $K\in \mathbb{R}^n$ is defined by a set of linear inequaities:
$$ \forall i \; 0\leq x_i \leq 1 $$
and
$ ...

**12**

votes

**0**answers

102 views

### Rational inscribed realization of the regular dodecahedron

While it is clear that the regular dodecahedron $D$ cannot be realized with all integer coordinates, it is easy to find a polytope, which is combinatorially equivalent (face lattice isomorphic) to $D$ ...

**9**

votes

**0**answers

152 views

### Determining convexity of a polygon from its Fourier coefficients

Consider an $n$-sided polygonal curve in the plane, represented by an ordered set of points $(x_0, x_1, \ldots, x_{n-1})$; line segments connect consecutive points and also $x_{n-1}$ to $x_0$. It is ...

**11**

votes

**1**answer

358 views

### Tiling by regular simplices

The plane can be tiled without gaps by congruent two-dimensional regular simplices (i.e., equilateral triangles). The three-dimensional Euclidean space cannot be tiled by congruent three-dimensional ...

**2**

votes

**1**answer

58 views

### Constructing a polygon of $n$ facets from a set of positive values representing the length of the facets [closed]

The input of my problem is a set of positive values $a=\{a_1,...,a_n\}$ where $n\geq 3$.
I want to construct an $n$-gon where the lengths of the $n$ facets are the values $a_i$ for $i=1,...,n$.
My ...

**1**

vote

**0**answers

235 views

### Reduction to some physical interpretation of this formula

Problem Given N 3-dimensional points which are {$p_1,p_2,..,p_n$} where $p_i = (x_i,y_i,z_i) $ . I have to find the value of the formula
$$ \sum \limits_{i=0}^n \sum \limits_{j=i+1}^n \frac{ \mid \...

**8**

votes

**1**answer

239 views

### Integer sets with forbidden differences

Given a finite set $S$ of positive integers, and a positive integer $n$, let $F(n,S)$ be the largest possible cardinality of a subset of {$1,2,\dots,n$} no two of whose elements differ by a number in $...

**1**

vote

**0**answers

24 views

### Homology of the subcomplexes of the “diamond shaped” sphere under 1-norm in $R^n$ as a simplicial complex

The 1-norm on $\mathbb{R}^n$ is defined by $\|v\| = |v_1| + |v_2| + \cdots + |v_n|$ for a vector $v = (v_1, \ldots, v_n) \in \mathbb R^n$.
The unit sphere $S^{n-1}_1$ under the 1-norm is a simplicial ...

**12**

votes

**0**answers

255 views

### Self-avoiding random walks that always turn

I am wondering if the statistics of self-avoiding random lattice-walks
on $\mathbb{Z}^2$
that turn left or right at each step (i.e., they cannot continue the
direction of the preceding step) have been ...

**13**

votes

**1**answer

288 views

### Exotic line arrangements

I would like to discuss the following problem. Hopefully, you will suggest to me some ideas and bibliography.
At first I will provide some basic definitions to set up the notation.
Let us consider ...

**38**

votes

**2**answers

1k views

### Can we find lattice polyhedra with faces of area 1,2,3,…?

I asked this question two months ago on MSE, where it earned the rare
Tumbleweed badge for garnering zero votes, zero answers, and 25 views over 61 days.
Perhaps justifiably so! Here I repeat it with ...

**43**

votes

**5**answers

1k views

### Tetris-like falling sticky disks

Suppose unit-radius disks fall vertically from $y=+\infty$,
one by one, and create a random jumble of disks above the $x$-axis.
When a falling disk hits another, it stops and sticks there.
Otherwise, ...

**25**

votes

**0**answers

526 views

### Tiling a square with rectangles

Is it possible to completely tile a square with different rectangles of integer sides but all with the same area?
The original problem, not requiring integer sides for rectangles, was proposed by Joe ...