The algebraic connectivity of a graph, which is the second-smallest eigenvalue of the Laplacian of the graph, is a measure of connectivity. We show that the problem of adding a specified number of edges to an input graph to maximize the algebraic connectivity of the augmented graph is NP-hard.

For a graph G of order n, the maximum nullity of G is defined to be the largest possible nullity over all real symmetric n × n matrices A whose (i, j)th entry (for i 6= j) is nonzero whenever {i, j} is an edge in G and is zero otherwise. Maximum nullity and the related parameter minimum rank of the same set of matrices have been studied extensively. A new parameter, maximum generic nullity, is ...

Let I be a n n binary image stored in a n n mesh of processors with one pixel per processor. Image I is k-width-connected if, informally, between any pair of 1-pixels there exists a path of width k (composed of 1-pixels only). We consider the problem of determining the largest integer k such that I is k-width-connected, and present an optimal O(n) time algorithm for the mesh architecture.

Recently, some sufficient conditions for a digraph to have maximum connectivity or high superconnectivity have been given in terms of a new parameter which can be thought of as a generalization of the girth of a graph. In this paper similar results are derived for bipartite digraphs and graphs showing that, in this case, all the known conditions can be improved. As a corollary, it is shown that...

Consider N entities to be classified (e.g., geographical areas), a matrix of dissimilarity between pairs of entities, a graph H with vertices associated with these entities such that the edges join the vertices corresponding to contiguous entities. The split of a cluster is the smallest dissimilarity between an entity of this cluster and an entity outside of it. The single-linkage algorithm (ig...

A generalized p-cycle is a digraph whose set of vertices is partitioned in p parts that are cyclically ordered in such a way that the vertices in one part are adjacent only to vertices in the next part. In this work, we mainly show the two following types of conditions in order to find generalized p-cycles with maximum connectivity: 1. For a new given parameter `, related to the number of short...

Let $Gamma_{n,kappa}$ be the class of all graphs with $ngeq3$ vertices and $kappageq2$ vertex connectivity. Denote by $Upsilon_{n,beta}$ the family of all connected graphs with $ngeq4$ vertices and matching number $beta$ where $2leqbetaleqlfloorfrac{n}{2}rfloor$. In the classes of graphs $Gamma_{n,kappa}$ and $Upsilon_{n,beta}$, the elements having maximum augmented Zagreb index are determined.

many graph theoretical parameters have been used to describe the vulnerability of communication networks, including toughness, binding number, rate of disruption, neighbor-connectivity, integrity, mean integrity, edgeconnectivity vector, l-connectivity and tenacity. in this paper we discuss integrity and its properties in vulnerability calculation. the integrity of a graph g, i(g), is defined t...

The average connectivity of a digraph is the average, over all ordered pairs of vertices, of the maximum number of internally disjoint directed paths connecting these vertices. Among the results in this paper, we determine the minimum average connectivity among all orientations of the complete multipartite graph K n1 ,n2, ... ,nk and the maximum average connectivity when all partite sets have t...

Many graph theoretical parameters have been used to describe the vulnerability of communication networks, including toughness, binding number, rate of disruption, neighbor-connectivity, integrity, mean integrity, edgeconnectivity vector, l-connectivity and tenacity. In this paper we discuss Integrity and its properties in vulnerability calculation. The integrity of a graph G, I(G), is defined t...