Computing the transitive closure in directed graphs is a fundamental graph problem. We consider the more restricted problem of computing the number of nodes reachable from every node and the size of the transitive closure. The fastest known transitive closure algorithms run in O(min{mn, n2.38}) time, where n is the number of nodes and m the number of edges in the graph. We present an O(m) time ...

Given a transitive orientation ~ G of a comparability graph G, a vertex of G is a source (sink) if it has indegree (outdegree) zero in ~ G, respectively. A source set of G is a subset of vertices formed by sources of some transitive orientation of G. A pair of subsets S; T V (G) is a source-sink pair of G when the vertices of S and T are sources and sinks, respectively, of some transitive orien...

A transitive decomposition is a pair ðG;PÞ where G is a graph and P is a partition of the arc set of G, such that there exists a group of automorphisms of G which leaves P invariant and transitively permutes the parts in P. This paper concerns transitive decompositions where the group is a primitive rank 3 group of ‘grid’ type. The graphs G in this case are either products or Cartesian products...

A Cayley (resp. bi-Cayley) graph on a dihedral group is called dihedrant bi-dihedrant). In 2000, classification of trivalent arc-transitive dihedrants was given by Marušič and Pisanski, several years later, non-arc-transitive order 4p or 8p (p prime) were classified Feng et al. As generalization these results, our first result presents dihedrants. Using this, complete vertex-transitive non-Cayl...

The present paper is devoted classification of $\mathrm {AT4}(p,p+2,r)$-graphs. There a unique {AT4}(p,p+2,r)$-graph with $p=2$, namely, the distance-transitive Soicher graph intersection array $\{56, 45, 16, 1;1, 8, 56\}$, whose local graphs are isomorphic to Gewirtz graph. existence an ${p>2}$ remains open question. It known that each strongly regular parameters $\big ((p+2)(p^2+4p+2),p(p+3),...

The connective constant μ(G) of a quasi-transitive graph G is the exponential growth rate of the number of self-avoiding walks from a given origin. We prove a locality theorem for connective constants, namely, that the connective constants of two graphs are close in value whenever the graphs agree on a large ball around the origin. The proof exploits a generalized bridge decomposition of self-a...

A theorem of A. Schrijver asserts that a d–regular bipartite graph on 2n vertices has at least ( (d− 1)d−1 dd−2 )n perfect matchings. L. Gurvits gave an extension of Schrijver’s theorem for matchings of density p. In this paper we give a stronger version of Gurvits’s theorem in the case of vertex-transitive bipartite graphs. This stronger version in particular implies that for every positive in...

This paper presents a solution of the polycirculant conjecture which states that every vertex-transitive graph G has an automorphism that permutes the vertices in cycles of the same length. This is done by identifying vertex-transitive graphs as coset graphs. For a coset graph H, an equivalence relation ∼ is defined on the vertices of cosets with classes as double cosets of the stabiliser and a...

A transitive decomposition is a pair (Γ,P) where Γ is a graph and P is a partition of the arc set of Γ such that there is a subgroup of automorphisms of Γ which leaves P invariant and transitively permutes the parts in P. In an earlier paper we gave a characterisation of G-transitive decompositions where Γ is the graph product Km×Km and G is a rank 3 group of product action type. This character...

In this paper we introduce some general necessary conditions for the existence of graph homomorphisms, which hold in both directed and undirected cases. Our method is a combination of Diaconis and Saloff– Coste comparison technique for Markov chains and a generalization of Haemers interlacing theorem. As some applications, we obtain a necessary condition for the spanning subgraph problem, which...