English

The Erd\H{o}s-Gy\'{a}rf\'{a}s function with respect to Gallai-colorings

Combinatorics 2022-03-23 v2

Abstract

For fixed pp and qq, an edge-coloring of the complete graph KnK_n is said to be a (p,q)(p, q)-coloring if every KpK_p receives at least qq distinct colors. The function f(n,p,q)f(n, p, q) is the minimum number of colors needed for KnK_n to have a (p,q)(p, q)-coloring. This function was introduced about 45 years ago, but was studied systematically by Erd\H{o}s and Gy\'{a}rf\'{a}s in 1997, and is now known as the Erd\H{o}s-Gy\'{a}rf\'{a}s function. In this paper, we study f(n,p,q)f(n, p, q) with respect to Gallai-colorings, where a Gallai-coloring is an edge-coloring of KnK_n without rainbow triangles. Combining the two concepts, we consider the function g(n,p,q)g(n, p, q) that is the minimum number of colors needed for a Gallai-(p,q)(p, q)-coloring of KnK_n. Using the anti-Ramsey number for K3K_3, we have that g(n,p,q)g(n, p, q) is nontrivial only for 2qp12\leq q\leq p-1. We give a general lower bound for this function and we study how this function falls off from being equal to n1n-1 when q=p1q=p-1 and p4p\geq 4 to being Θ(logn)\Theta(\log n) when q=2q = 2. In particular, for appropriate pp and nn, we prove that g=ncg=n-c when q=pcq=p-c and c{1,2}c\in \{1,2\}, gg is at most a fractional power of nn when q=p1q=\lfloor\sqrt{p-1}\rfloor, and gg is logarithmic in nn when 2qlog2(p1)+12\leq q\leq \lfloor\log_2 (p-1)\rfloor+1.

Keywords

Cite

@article{arxiv.2011.01592,
  title  = {The Erd\H{o}s-Gy\'{a}rf\'{a}s function with respect to Gallai-colorings},
  author = {Xihe Li and Hajo Broersma and Ligong Wang},
  journal= {arXiv preprint arXiv:2011.01592},
  year   = {2022}
}

Comments

25 pages