The Slope Polynomial and Collinear Points in Permutations

Collinear Points in Permutations

Consider the following problem: how many collinear triples of points must a transversal of (Z/nZ)^2 have? This question is connected with venerable issues in discrete geometry. We show that the answer, for n prime, is between (n-1)/4 and (n-1)/2, and consider an analogous question for collinear quadruples. We conjecture that the upper bound is the truth and suggest several other interesting problems in this area.

Collinear Triple Hypergraphs and the Finite Plane Kakeya Problem

We show that the problem of counting collinear points in a permutation (previously considered by the author and J. Solymosi in "Collinear Points in Permutations", 2005) and the well-known finite plane Kakeya problem are intimately connected. Via counting arguments and by studying the hypergraph of collinear triples we show a new lower bound (5q/14 + O(1)) for the number of collinear triples of a permutation of GF(q) and a new lower bound (q(q + 1)/2 + 5q/14 + O(1)) on the size of the smallest Besicovitch set in GF(q)^2. Several interesting questions about the structure of the collinear triple …

On the number of collinear triples in permutations

Let $α:\mathbb{Z}_n\to\mathbb{Z}_n$ be a permutation and $Ψ(α)$ be the number of collinear triples modulo $n$ in the graph of $α$. Cooper and Solymosi had given by induction the bound $\min_αΨ(α)\geq\lceil(n-1)/4\rceil$ when $n$ is a prime number. The main purpose of this paper is to give a direct proof of that bound. Besides, the expected number of collinear triples a permutation can have is also been determined.

Collinear triples in permutations

Let $α:\mathbb{F}_q\to\mathbb{F}_q$ be a permutation and $Ψ(α)$ be the number of collinear triples in the graph of $α$, where $\mathbb{F}_q$ denotes a finite field of $q$ elements. When $q$ is odd Cooper and Solymosi once proved $Ψ(α)\geq(q-1)/4$ and conjectured the sharp bound should be $Ψ(α)\geq(q-1)/2$. In this note we indicate that the Cooper-Solymosi conjecture is true.

最小化共线三元组数量的置换

Permutations minimizing the number of collinear triples

本文刻画了有限域上使图中共线三元组数量最少的置换，确定字典序最小者，证实 Cooper-Solymosi 猜想，并探讨其与正交拉丁方及有限仿射平面的联系。

Affine permutations and rational slope parking functions

We introduce a new approach to the enumeration of rational slope parking functions with respect to the area and a generalized dinv statistics, and relate the combinatorics of parking functions to that of affine permutations. We relate our construction to two previously known combinatorial constructions: Haglund's bijection exchanging the pairs of statistics (area,dinv) and (bounce,area) on Dyck paths, and Pak-Stanley labeling of the regions of k-Shi hyperplane arrangements by k-parking functions. Essentially, our approach can be viewed as a generalization and a unification of these two constru…