Some upper bounds for the signless Laplacian spectral radius of digraphs

TL;DR

This paper establishes new upper bounds for the signless Laplacian spectral radius of digraphs, relating it to outdegrees and average 2-outdegrees, enhancing understanding of spectral properties in directed graphs.

Contribution

The paper introduces novel upper bounds for the signless Laplacian spectral radius of digraphs, incorporating outdegree and average 2-outdegree measures.

Findings

Derived upper bounds for q(G) based on outdegrees.

Established bounds involving average 2-outdegrees.

Provided theoretical insights into spectral radius limitations.

Abstract

Let $G=(V(G) ,E(G))$ be a digraph without loops and multiarcs, where $V(G)=\{v_1,v_2,\ldots,v_n\}$ and $E(G)$ are the vertex set and the arc set of $G$, respectively. Let $d_i^{+}$ be the outdegree of the vertex $v_i$. Let $A(G)$ be the adjacency matrix of $G$ and $D(G)=\textrm{diag}(d_1^{+},d_2^{+},\ldots,d_n^{+})$ be the diagonal matrix with outdegrees of the vertices of $G$. Then we call $Q(G)=D(G)+A(G)$ the signless Laplacian matrix of $G$. The spectral radius of $Q(G)$ is called the signless Laplacian spectral radius of $G$, denoted by $q(G)$. In this paper, some upper bounds for $q(G)$ are obtained. Furthermore, some upper bounds on $q(G)$ involving outdegrees and the average 2-outdegrees of the vertices of $G$ are also derived.