On the sum of the largest $A_{\alpha }$-eigenvalues of graphs

Abstract

For every real $0\le \alpha \le 1$, Nikiforov defined the $A_{\alpha }$-matrix of a graph $G$ as $A_{\alpha }(G)=\alpha D(G)+(1-\alpha )A(G)$, where $A(G)$ and $D(G)$ are the adjacency matrix and the degree diagonal matrix of a graph $G$, respectively. The eigenvalues of $A_{\alpha }(G)$ are called the $A_{\alpha }$-eigenvalues of $G$. Let $S_k(A_{\alpha }(G))$ be the sum of $k$ largest $A_{\alpha }$-eigenvalues of $G$. In this paper, we present several upper and lower bounds on $S_k(A_{\alpha }(G))$ and characterize the extremal graphs for certain cases, which can be regard as a common generalization of the sum of $k$ largest eigenvalues of adjacency matrix and signless Laplacian matrix of graphs. In addition, some graph operations on $S_k(A_{\alpha }(G))$ are presented.

29 pages, 1 figure