On the $\hat{I}\pm$-spectral radius of graphs

Abstract

For $0\le \hat{I}\pm \le 1$, Nikiforov proposed to study the spectral properties of the family of matrices $A_{\hat{I}}\pm (G)=\hat{I}\pm D(G)+(1-\hat{I}\pm )A(G)$ of a graph $G$, where $D(G)$ is the degree diagonal matrix and $A(G)$ is the adjacency matrix. The $\hat{I}\pm$-spectral radius of $G$ is the largest eigenvalue of $A_{\hat{I}}\pm (G)$. We give upper bounds for $\hat{I}\pm$-spectral radius for unicyclic graphs $G$ with maximum degree $\hat{I}”\ge 2$, connected irregular graphs with given maximum degree and and some other graph parameters, and graphs with given domination number, respectively. We determine the unique tree with second maximum $\hat{I}\pm$-spectral radius among trees, and the unique tree with maximum $\hat{I}\pm$-spectral radius among trees with given diameter. For a graph with two pendant paths at a vertex or at two adjacent vertex, we prove results concerning the behavior of the $\hat{I}\pm$-spectral radius under relocation of a pendant edge in a pendant path. We also determine the unique graphs such that the difference between the maximum degree and the $\hat{I}\pm$-spectral radius is maximum among trees, unicyclic graphs and non-bipartite graphs, respectively.