We construct infinitely many connected, circulant digraphs of outdegree three that have no hamiltonian circuit. All of our examples have an even number of vertices, and our examples are of two types: either every vertex in the digraph is adjacent to two diametrically opposite vertices, or every vertex is adjacent to the vertex diametrically opposite to itself.

In this survey we overview known results on the strong subgraph [Formula: see text]-connectivity and text]-arc-connectivity of digraphs. After an introductory section, paper is divided into four sections: basic results, algorithms complexity, sharp bounds for text]-(arc-)connectivity, minimally text]-(arc-) connected This contains several conjectures open problems further study.

For designing reliable and efficient communications networks, the problem of constructing a maximally connected d-regular digraph (directed graph) with a small diameter is investigated. A maximally connected d-regular digraph with a diameter at most two larger than the lower bound for any number of nodes n > 2d and any d > 3 is constructed. Since the diameter of this digraph is quasiminimal (at...

In this work, first, we present sufficient conditions for a bipartite digraph to attain optimum values of a stronger measure of connectivity, the so-called superconnectivity. To be more precise, we study the problem of disconnecting a maximally connected bipartite (di)graph by removing nontrivial subsets of vertices or edges. Within this framework, both an upper-bound on the diameter and Chartr...

The restricted arc-connectivity λ′ of a strongly connected digraph G is the minimum cardinality of an arc cut F in G such that every strongly connected component of G−F contains at least two vertices. This paper shows that for a d-regular strongly connected digraph with order n and diameter k ≥ 4, if λ′ exists, then λ′(G) ≥ min { (n − dk−1)(d− 1) dk−1 + d− 2 , 2d− 2 } As consequences, the restr...

A properly connected coloring of a given graph G is one that ensures that every two vertices are the ends of a properly colored path. The proper connection number of G is the minimum number of colors in such a coloring. We study the proper connection number for edge and vertex colorings, in undirected and directed graphs, respectively. More precisely, we initiate the study of the complexity of ...

This is intended as a survey article covering recent developments in the area of hamiltonian graphs, that is, graphs containing a spanning cycle. This article also contains some material on related topics such as traceable, hamiltonian-connected and pancyclic graphs and digraphs, as well as an extensive bibliography of papers in the area. 1. Supported by O.N.R. contract number N000014-88-K-0070.

The global dynamics of coupled systems of differential equations defined on an interaction network are investigated. Local dynamics at each vertex, when interactions are absent, are assumed to be simple: solutions to each vertex system are assumed to converge to an equilibrium, either on the boundary or in the interior of the feasible region. The interest is to investigate the collective behavi...

In this paper the properties of node-node adjacency matrix in acyclic digraphs are considered. It is shown that topological ordering and node-node adjacency matrix are closely related. In fact, first the one to one correspondence between upper triangularity of node-node adjacency matrix and existence of directed cycles in digraphs is proved and then with this correspondence other properties of ...