On spectral radius and energy of extended adjacency matrix of graphs

摘要

Let G be a graph of order n. For i=1,2,…,n, let di be the degree of the vertex vi of G. The extended adjacency matrix Aex of G is defined so that its (i, j)-entry is equal to 12(didj+djdi) if the vertices vi and vj are adjacent, and 0 otherwise,Yang et al. (1994). The spectral radius η1 and the energy Eex of the Aex-matrix are examined. Lower and upper bounds on η1 and Eex are obtained, and the respective extremal graphs characterized.