Bounds on parameters of minimally nonlinear patterns

P. A. CrowdMath¹

¹MIT

The electronic journal of combinatorics, Tome 25 (2018) no. 1

Résumé

Let $ex(n, P)$ be the maximum possible number of ones in any 0-1 matrix of dimensions $n \times n$ that avoids $P$. Matrix $P$ is called minimally non-linear if $ex(n, P) \neq O(n)$ but $ex(n, P') = O(n)$ for every proper subpattern $P'$ of $P$. We prove that the ratio between the length and width of any minimally non-linear 0-1 matrix is at most $4$, and that a minimally non-linear 0-1 matrix with $k$ rows has at most $5k-3$ ones. We also obtain an upper bound on the number of minimally non-linear 0-1 matrices with $k$ rows.In addition, we prove corresponding bounds for minimally non-linear ordered graphs. The minimal non-linearity that we investigate for ordered graphs is for the extremal function $ex_{<}(n, G)$, which is the maximum possible number of edges in any ordered graph on $n$ vertices with no ordered subgraph isomorphic to $G$.

Détail

DOI : 10.37236/6735

Classification : 05D99
Mots-clés : extremal functions, ordered graphs, 0-1 matrices, minimally non-linear, pattern avoidance, generalized Davenport-Schinzel sequences