For a graph G = (V , E), a subset D V ðGÞ is said to be distance two-dominating set in G if for each vertex u 2 V D, there exists a vertex v 2 D such that dðu; vÞ 2. The minimum cardinality of a distance two-dominating set in G is called a distance twodomination number and is denoted by c2ðGÞ. In this note we obtain various upper bounds for c2ðGÞ and characterize the classes of graphs attaining...

<abstract><p>Let $ A(G) and D(G) be the adjacency matrix degree diagonal of a graph G $, respectively. For any real number \alpha \in[0, 1] Nikiforov defined A_{\alpha} $-matrix as A_{\alpha}(G) = D(G)+(1-\alpha)A(G) $. Let S_k(A_{\alpha}(G)) sum k largest eigenvalues In this paper, some bounds on are obtained, which not only extends results signless Laplacian matrix, but it also gi...

We extend our previous survey of properties of spectra of signless Laplacians of graphs. Some new bounds for eigenvalues are given, and the main result concerns the graphs whose largest eigenvalue is maximal among the graphs with fixed numbers of vertices and edges. The results are presented in the context of a number of computer-generated conjectures.