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Let Γ = ( G , σ ) be a signed graph, where G is the underlying simple graph and σ : E ( G ) → { + , − } is the sign function on the edges of G . In this paper we consider the spectral characterization problem extended to the adjacency matrix and Laplacian matrix of signed graphs. After giving some basic results, we study the spectral determination of signed lollipop graphs, and we show that any signed lollipop graph is determined by the spectrum of its Laplacian matrix. [ABSTRACT FROM AUTHOR]

Abstract: A generalized Bethe tree is a rooted tree in which vertices at the same level have the same degree. For let be a generalized Bethe tree of levels and let such that (1) the edges of connecting vertices at consecutive levels have the same weight, and (2) for , each set of children of at the level defines a clique in which the edges have weight For let be the graph obtained from and the cliques at the levels for all Let be the graph obtained from the graphs joined at their respective roots. We give a complete characterization of the eigenvalues, including their multiplicities, of the Laplacian, signless Laplacian and adjacency matrices of the graph . Finally, we characterize the normalized Laplacian eigenvalues when is an unweighted graph. [Copyright &y& Elsevier]

Abstract: We characterize the eigenvalues and energy of the line graph whenever is (i) a generalized Bethe tree, (ii) a Bethe tree, (iii) a tree defined by generalized Bethe trees attached to a path, (iv) a tree defined by generalized Bethe trees having a common root, (v) a graph defined by copies of a generalized Bethe tree attached to a cycle and (vi) a graph defined by copies of a star attached to a cycle; in this case, explicit formulas for the eigenvalues and energy of are derived. [Copyright &y& Elsevier]

Abstract: Of interest here is a characterization of the undirected graphs G such that the Laplacian matrix associated with G can be diagonalized by some Hadamard matrix. Many interesting and fundamental properties are presented for such graphs along with a partial characterization of the cographs that have this property. [Copyright &y& Elsevier]

Abstract: A Bethe tree of levels, , is a rooted tree such that the root vertex has degree , the vertices from level to have degree and the vertices at level are leaves. In this paper, we obtain a recurrence relation for the characteristic polynomial and the Laplacian characteristic polynomial of Bethe trees. As an application, we prove that there are no integral Bethe trees except for the star , and we obtain a recurrence relation for the Laplacian-energy-like invariant of Bethe trees. [Copyright &y& Elsevier]

Abstract: Let G be a simple graph. Let and denote the largest eigenvalue of the adjacency matrix and the Laplacian matrix of G, respectively. Let denote the largest vertex degree. If G has just one cycle, thenThe equality holds if and only if . AndThe equality holds if and only if , n is even. [Copyright &y& Elsevier]

Abstract: The higher Randić index R t (G) of a simple graph G is defined aswhere δ i denotes the degree of the vertex i and i 1 i 2⋯i t+1 runs over all paths of length t in G. In [J.A. Rodríguez, A spectral approach to the Randić index, Linear Algebra Appl. 400 (2005) 339–344], the lower and upper bound on R 1(G) was determined in terms of a kind of Laplacian spectra, and the lower and upper bound on R 2(G) were done in terms of kinds of adjacency and Laplacian spectra. In this paper we characterize the graphs which achieve the upper or lower bounds of R 1(G) and R 2(G), respectively. [Copyright &y& Elsevier]