Walks and the spectral radius of graphs

AbstractGiven a graph G, write μ(G) for the largest eigenvalue of its adjacency matrix, ω(G) for its clique number, and wk(G) for the number of its k-walks. We prove that the inequalitieswq+r(G)wq(G)⩽μr(G)⩽ω(G)-1ω(G)wr(G)hold for all r>0 and odd q>0. We also generalize a number of other bounds on μ(G) and characterize semiregular and pseudo-regular graphs in spectral terms