On the largest eigenvalue of a mixed graph with partial orientation

Abstract

Let $G$ be a connected graph and let $T$ be a spanning tree of $G$. A partial orientation $\sigma$ of $G$ respect to $T$ is an orientation of the edges of $G$ except those edges of $T$, the resulting graph associated with which is denoted by $G_T^\sigma$. In this paper we prove that there exists a partial orientation $\sigma$ of $G$ respect to $T$ such that the largest eigenvalue of the Hermitian adjacency matrix of $G_T^\sigma$ is at most the largest absolute value of the roots of the matching polynomial of $G$.