A Cvetković-type Theorem for coloring of digraphs

Abstract

In 1972, Cvetković proved that if G is an n-vertex simple graph with the chromatic number k, then its spectral radius is at most the spectral radius of the n-vertex balanced complete k-partite graph. In this paper, we analyze the characteristic polynomial of a digraph D to prove a tight upper bound for the spectral radius of D in terms of the number of vertices and the chromatic number of D; we also characterize when equality holds. This provides a simple proof of a result by Lin and Shu [6].