English

Distribution of colors in Gallai colorings

Combinatorics 2020-02-03 v4

Abstract

A Gallai coloring is an edge coloring that avoids triangles colored with three different colors. Given integers e1e2eke_1\ge e_2 \ge \dots \ge e_k with i=1kei=(n2)\sum_{i=1}^ke_i={n \choose 2} for some nn, does there exist a Gallai kk-coloring of KnK_n with eie_i edges in color ii? In this paper, we give several sufficient conditions and one necessary condition to guarantee a positive answer to the above question. In particular, we prove the existence of a Gallai-coloring if e1ek1e_1-e_k\le 1 and kn/2k \le \lfloor n/2\rfloor. We prove that for any integer k3k\ge 3 there is a (unique) integer g(k)g(k) with the following property: there exists a Gallai kk-coloring of KnK_n with eie_i edges in color ii for every e1eke_1\le\dots \le e_k satisfying i=1kei=(n2)\sum_{i=1}^ke_i={n\choose 2}, if and only if ng(k)n\ge g(k). We show that g(3)=5g(3)=5, g(4)=8g(4)=8, and 2k2g(k)8k2+12k-2\le g(k)\le 8k^2+1 for every k3k\ge 3.

Keywords

Cite

@article{arxiv.1903.04380,
  title  = {Distribution of colors in Gallai colorings},
  author = {András Gyárfás and Dömötör Pálvölgyi and Balázs Patkós and Matthew Wales},
  journal= {arXiv preprint arXiv:1903.04380},
  year   = {2020}
}