All Questions
Tagged with mg.metric-geometry nt.number-theory
86 questions
7
votes
0
answers
165
views
Lonely globe trotters
In analogy with the lonely runners conjecture,
imagine "globe trotters" each traveling on a longitudinal great circle at different
(constant, positive) speeds. Each "trotter" ...
- 151k
1
vote
0
answers
114
views
A circle is inscribed in a triangle, with three other circles in the corner regions. The radii are integers. Possible values of the largest radius?
Originally posted at MSE.
A circle with integer radius $R$ is inscribed in a triangle. Three other circles with integer radii $a,b,c$ are each tangent to the large circle and two sides of the ...
- 3,527
1
vote
0
answers
52
views
'Self-similar and perfect' partitions of planar regions
Definition: A partition of a planar figure into finitely many pieces that are all similar to itself and also mutually non-congruent may be called a self-similar perfect partition.
A classical example ...
- 5,979
1
vote
0
answers
100
views
Perfect 'cuboiding' of cubes and cuboids
We try to add a bit to ref 2 listed below. In this post, by 'cuboid', we mean only rectangular cuboids - hexahedra with all faces rectangles and adjacent faces meeting only at right angles. A special ...
- 5,979
4
votes
1
answer
438
views
Perfect squaring of rectangles
A perfect squaring of a rectangle may be defined as a partition of the rectangle into finitely many squares all of which are mutually non-congruent. https://en.wikipedia.org/wiki/Squaring_the_square ...
- 5,979
9
votes
0
answers
187
views
Cubing the cube - as 'perfectly' as possible
Ref: https://en.wikipedia.org/wiki/Squaring_the_square
A perfect cubing of a cube is a partition of the cube into some finite number of smaller cubes that are pair-wise non-congruent. The above page ...
- 5,979
3
votes
1
answer
366
views
Illumination from visible lattice points with inverse square intensity
It is well known that the number of $\mathbb{Z}^2$ lattice points visible from
the origin is $6/\pi^2$, about $61$%.
See, e.g.,
What fraction of the integer lattice can be seen from the origin?.
I am ...
- 151k
4
votes
0
answers
111
views
Advice on results for balls on regular $N$-dimensional grids
I have obtained some results regarding balls on regular $N$-dimensional grids. I would like expert opinion on wether the results are significant or interesting enough for (trying to) publish them in a ...
- 337
3
votes
1
answer
954
views
A geometric proof that there are infinitely many primes?
Let $e_d$ be the $d$-th standard-basis vector in the Hilbert space $H=l_2(\mathbb{N})$.
Let $h(n) = J_2(n)$ be the second Jordan totient function, defined by:
$$J_2(n) = n^2 \prod_{p|n}(1-1/p^2)$$
...
- 3,064
2
votes
1
answer
588
views
Kissing number lower bound vs. upper bound - precise meanings?
According to en.wikipedia.org, https://en.wikipedia.org/wiki/Kissing_number#Some_known_bounds
It says the kissing numbers $K$ have lower bound $K_L$ and upper bound $K_S$:
$$
K_L < K < K_U.
$$
I ...
- 447
0
votes
1
answer
199
views
Leech lattice shortest vector vs other 23 cases and E8 cases
In this paper by Viazovska, she said that:
"The E8-lattice sphere packing 𝒫E8 is the union of open Euclidean balls with centers at
the lattice points and radius $1/\sqrt{2}$." So I think ...
- 447
7
votes
1
answer
497
views
Is there a bicyclic irregular pentagon in integers?
Is there a bicyclic irregular pentagon in integers, i.e. is there a pentagon, the length of each side is integer and unique such that it has a circumcircle and an inner circle as well?
If it does ...
- 71
1
vote
0
answers
77
views
Lattice packing
Let $\Lambda$ be a lattice in $R^n$ and $R>0$ a real number.
Consider the number $N$ of points in $\Lambda$ of norm less than $R$. Let $R$ goes to infinity. What can be said about the asymptotic ...
- 237
1
vote
0
answers
142
views
A question about Roger Penrose's spin networks and mathematical formalization?
Let $a,b,c$ be "units" in the spin network.
Then there are there are the following three requirements to fulfill (according to the relevant Wikipedia entry):
$a,b,c \in \mathbb{N}$
Triangle ...
- 3,064
2
votes
0
answers
95
views
Is there an exact solution for the number of points within a circle of radius r for an honeycomb lattice?
I want to ask if exists an exact solution for the number of points within a circle of radius r for an honeycomb lattice.
I know that it is exist for an square lattice https://mathworld.wolfram.com/...
- 31
0
votes
1
answer
937
views
The exact number of points within a circle of radius r centered on a lattice point in a hexagonal lattice? Review expression Gauss circle problem
In the case of a square lattice, the exact number of points within a circle of radius r centered in the center is (see: http://mathworld.wolfram.com/GausssCircleProblem.html:
$$N(r)=1+4Floor(r)+4 \...
- 31
8
votes
1
answer
362
views
Is the set of powerful numbers piecewise syndetic?
Recall that a subset $A \subset \mathbb Z_+$ of positive integers syndetic if there exists a $d>0$ such that every positive integer has distance at most $d$ to an element of $A$. It is called ...
- 11.9k
1
vote
0
answers
81
views
Intersecting lattices with surfaces in R^d
Let us fix some bounded surface $S\subset \mathbb{R}^d$. Let $x_1,\ldots, x_m$ be some non-zero vectors in $\mathbb{R}^d$. I am interested is the maximum number of points that the lattice $L_m=\{\sum ...
- 2,288
16
votes
1
answer
533
views
Is there a degenerate simplex in $\mathbb{R}^{8 k-1}$ with odd integer edge lengths?
The Cayley-Menger determinant gives the squared volume of a simplex in $\mathbb{R}^n$ as a function of its $n(n+1)/2$ edge lengths:
$$v_n^2 = \frac{(-1)^{n+1}}{(n!)^2 2^n}
\begin{vmatrix}
0&d_{01}^...
- 2,902
5
votes
2
answers
446
views
Lattices containing $A_n$ and $D_n$
How many lattices are there which contain both the $A_n$ and $D_n$ lattices of the same dimension as sublattices? So far, I’ve found examples in 1D, 3D, 8D, and 24D.
- 2,773
9
votes
1
answer
204
views
Which unimodular lattices $L\subset \mathbb R^2$ minimize $f_t(L):=\sum_{ v\in L} e^{-t \|v\|_2}$? (for parameters $t>0$)
$\DeclareMathOperator\SL{SL}\DeclareMathOperator\SO{SO}$Consider the lattices in $\SL(2,\mathbb R)(\mathbb Z^2)$ up to rotation. The space of such lattices can be identified with the modular surface $\...
- 241
8
votes
2
answers
803
views
a Littlewood–Offord-type problem concerning the "cubical lattice"
Fix even $n$ and consider the boolean function $f : \{0, 1\}^n \rightarrow \{0, 1\}$, $f : (x_0, \ldots , x_{n - 1}) \mapsto (x_0 \vee x_1) \wedge (x_2 \vee x_3) \wedge \cdots \wedge (x_{n - 2} \vee ...
- 63
6
votes
2
answers
544
views
On circles and ellipses drawn on an infinite planar square lattice
Consider a plane with a square lattice formed by all points with both coordinates as integers. As can be easily seen, a simple parabola can be found that passes through infinitely many of the square ...
- 5,979
4
votes
0
answers
396
views
Dense sets in $\Bbb{R}^2$ with rational distance
We call a subset $S\subset \Bbb{R}^2$ rationally distanced if all $s_1,s_2 \in S$ have rational Euclidean distance.
The Erdos-Ulam conjecture asks if there is a dense subset of $\Bbb{R}^2$ which is ...
- 3,499
2
votes
1
answer
600
views
A geometric approach to the odd perfect number problem?
Let $e_d$ be the $d$-th standard-basis vector in the Hilbert space $H=l_2(\mathbb{N})$.
Let $h(n) = J_2(n)$ be the second Jordan totient function.
Define:
$$\phi(n) = \frac{1}{n} \sum_{d|n}\sqrt{h(d)}...
- 3,064
7
votes
0
answers
346
views
The space of $p$-adic norms
The 1963 paper by Goldman and Iwahori The space of $p$-adic norms deals with the space of norms on a finite dimensional vector space $E$ over a locally compact complete discrete valuation field $K$. I ...
- 433
3
votes
1
answer
302
views
number of integer points inside a triangle and its area
Let $T$ be a triangle in $\mathbb{R}^2$ defined by $y = \alpha x$, $y = \beta$ and $x = \gamma$ where
$\alpha, \beta, \gamma \in \mathbb{R}_{>0}$. I am interested in obtaining an estimate for the ...
- 3,625
11
votes
0
answers
307
views
Entropy, magnitude, diversity of finite metric spaces in number theory
I was reading the article by Tom Leinster, (Maximizing
diversity in biology and beyond, arXiv link), and find it very interesting.
Since I was searching for entropies of finite metric spaces I found
...
user6671
3
votes
1
answer
818
views
Has anyone studied spaces based on the number of centers circles have on them?
I have been away from math for a while so be gentle if this is not very rigorous or if I am redefining already defined objects. The essential question that started me on this was the following. In the ...
- 39
24
votes
4
answers
2k
views
A reinterpretation of the $abc$ - conjecture in terms of metric spaces?
I hope it is appropriate to ask this question here:
One formulation of the abc-conjecture is
$$ c < \text{rad}(abc)^2$$
where $\gcd(a,b)=1$ and $c=a+b$. This is equivalent to ($a,b$ being ...
user6671
10
votes
1
answer
648
views
Does every positive-definite integral lattice admit an angle-preserving homomorphism into $\Bbb Z^n$ for some $n$?
Some initial clarifications
By lattice I mean an additive subgroup of $\mathbb R^n$ which is isomorphic to $\mathbb Z^n$ and has full rank (i.e. spans $\Bbb R^n$ when considered as set of vectors). A ...
- 13.6k
2
votes
4
answers
997
views
Why does $\sqrt 5$ occur in manageable situations of these scenarios? [closed]
Banach-Mazur distance between $P_5$ and $P_3$ is $d(P_5,P_3)=1+\frac{\sqrt5}2$ where $P_n$ is regular polygon in $n$ sides https://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=7968198&tag=...
- 1,826
3
votes
0
answers
310
views
Upper bound on the number of lattice points on the intersection of a hyperplane and a sphere
Let $R>0$, $\overrightarrow{\alpha} \in \mathbb{R}^{d}$. Consider the intersection $T$of $RS^{d-1}$ and the hyperplane $\overrightarrow{\alpha} \cdot \overrightarrow{x} = n$. What is the best known ...
- 461
6
votes
0
answers
176
views
Approximating a ray with an integer lattice point
Take $X$ uniform on the unit sphere in $\mathbb{R}^n.$ For $r>0$, take $S_r=\{x\in \mathbb{Z}^n: \sum_i x_i^2 \leq r^2\}.$
With $\|\cdot \|$ the 2-norm, what is the distribution (or at least the ...
17
votes
0
answers
1k
views
Almost monochromatic point sets
There are many sort of equivalent theorems about monochromatic configurations in finite colorings, such as Van der Waerden, Hales-Jewett or Gallai's theorem, the latter of which states that in a ...
- 18.8k
3
votes
1
answer
118
views
Question arise from kissing number in 2 dimension
I'm considering an extended problem of kissing number in $\mathbb{R}^2$.
Suppose I have a given disc $\mathcal{D}$ of radius 1/2 and infinitely many discs all of radius 1/2 and all these discs and ...
- 1,495
1
vote
0
answers
196
views
Squares as sum of squares
For which positive integers n is $n^2$ the sum of precisely n smaller positive squares?
Of these n x n squares, which can be actually cut into n smaller squares?
- 3,707
9
votes
0
answers
365
views
How to count integer lattice points close to a subspace of $\mathbb R^n$?
Consider $m$ linearly independent vectors in $n$-dimensional Euclidean space, $v_1,...,v_m \in \mathbb R^n$ where $1\leq m<n$, and let $U := {\rm span}(v_1,...,v_m)$ denote the $m$-dimensional ...
- 686
5
votes
1
answer
188
views
Example of a non-arithmetic Veech surface (other than regular polygon)?
I am reading this paper of Avila and Delecroix of the billiard flow on polygonal surfaces, but I have to get through some basic definitions first. What is a non-arithmetic Veech surface?
A Veech ...
- 22.8k
6
votes
1
answer
237
views
Current interest in geometric properties of Hilbert fundamental domains
Harvey Cohn published several articles in the 1960's analyzing geometric properties of fundamental domains for Hilbert modular surfaces.
H. Cohn, "On the shape of the fundamental domain of the ...
- 2,436
1
vote
1
answer
145
views
More on divisibility
This is a fuzzier follow-up to this question. Again, we construct the graph whose vertices are integers from $1$ to $n,$ and two vertices are connected whenever one of the corresponding integers ...
- 96.4k
3
votes
0
answers
145
views
How much can analogy between $\Bbb Z$ and $\Bbb F_q[t]$ work out to give better distance measures in information theory?
Let $x$ be transmitted symbol and $y$ be received symbol and $n$ be noise Given $y=x+n$ where symbols $x,y,n$ are in $\Bbb K$. If $\Bbb K=\Bbb Z$ then we take $|n|$ to be the magnitude of noise while ...
- 13.9k
11
votes
4
answers
447
views
Sequential addition of points on a circle, optimizing asymptotic packing radius
Suppose I have to put $N$ points $x_1, x_2, \ldots, x_N$ on the circle $S^1$ of length 1 so as to achieve the largest minimum separation (packing radius). The optimal solution is the equally spaced ...
- 5,971
8
votes
1
answer
280
views
Hyperbolic planes inside hyperbolic 3-space quotients
Let $\mathcal{H}_2 = \{(x,t) \in \mathbf{R}^2: t > 0\}$ be the upper half-plane, and let $\mathcal{H}_3$ be the hyperbolic 3-space $\{(x,t) \in \mathbf{C} \times \mathbf{R}: t > 0\}$. Clearly $\...
- 37k
5
votes
0
answers
107
views
How well can a rotation separate lattice vectors of equal norm in Z^d?
I'm interested in rotations $R$ that maximally separate integral lattice vectors of equal norm. This question is preliminary, and regards the scaling of those separations as norm goes to infinity.
...
- 271
7
votes
1
answer
642
views
volume over a hypercube, over simplex: twist by Euler numbers
Let $\square_n=\{(x_1,\dots,x_n): 0\leq x_i\leq1,\, \forall i\}$ be an $n$-dimensional unit hypercube, and let $\Delta_n=\{(u_1,\dots,u_n):u_1+\cdots+u_n\leq\frac{\pi}2,\, u_i\geq0,\, \forall i\}$ be $...
- 43.2k
6
votes
2
answers
473
views
rate of equidistribution of the horocycle flow for $SL(2, \mathbb{Z})$
I know that for any Fuchsian group $\Gamma$, there is a spectral gap, which leads to
$$ \left| \int_0^1 F(x + iy) \, dx - \int_{\Gamma \backslash \mathbb{H}} F \, \frac{dx \, dy}{y^2} \right| < ...
- 22.8k
9
votes
2
answers
598
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 ...
- 3,707
21
votes
1
answer
1k
views
Sphere packings : what next after the recent breakthrough of Viazovska (et al.)?
Given the march 2016 breakthrough concerning sphere packings by Viazovska for the case of dimension 8, and by Cohn, Kumar, Miller, Radchenko and Viazovska for the case of dimension 24, it follows that ...
- 883
1
vote
0
answers
79
views
Completely incongruent box partitions
Let $B$ be a rectangular box with corners in $\mathbb{Z}^d$
and sides parallel to the axes.
A completely incongruent partition of $B$ is a partition into
$d$-dimensional boxes, each of whose integer ...
- 151k