Let G be a simple graph with vertex set {v1, v2, … , vn}. The common neighborhood graph of G, denoted by con(G), is a graph with vertex set {v1, v2, … , vn}, in which two vertices are adjacent if and only if they have at least one common neighbor in the graph G. In this paper, we compute the common neighborhood of some composite graphs. In continue, we investigate the relation between hamiltoni...

A cycle double cover (CDC) of an undirected graph is a collection of the graph’s cycles such that every edge of the graph belongs to exactly two cycles. We describe a constructive method for generating all the cubic graphs that have a 6-CDC (a CDC in which every cycle has length 6). We also prove that all such graphs have a Hamiltonian cycle.

Consider factorizations into transpositions of an n-cycle in the symmetric group Sn. To every such factorization we assign a monomial in variables wij that retains the transpositions used, but forgets their order. Summing over all possible factorizations of n-cycles we obtain a polynomial that happens to admit a closed expression. From this expression we deduce a formula for the number of 1-fac...

Consider factorizations into transpositions of an n-cycle in the symmetric group Sn. To every such factorization we assign a monomial in variables wij that retains the transpositions used, but forgets their order. Summing over all possible factorizations of n-cycles we obtain a polynomial that happens to admit a closed expression. From this expression we deduce a formula for the number of 1-fac...

In 1978 Erdős, Faudree, Rousseau, and Schelp conjectured that r (Cp, Kr) = (p − 1) (r − 1) + 1. for every p ≥ r ≥ 3, except for p = q = 3. This has been proved for r ≤ 6, and for p ≥ r 2 − 2r. In this note we prove the conjecture for p ≥ 4r + 2.

For graphs G and H, a map f : V (G) 7→ V (H) is a homomorphism if f preserves adjacency. Let Hom(G,H) denote the set of all homomorphisms from G into H. In this paper, we proved that for a simple graph G with n = |V (G)| and for k with n ≥ k ≥ 5, if the odd girth of G is at least 2k+1 and if the minimum degree δ(G) > 2n/(2k+3), then Hom(G,Z2k+1) 6= ∅, where Z2k+1 denotes the cycle of length 2k ...

For a positive integer n, let G be Kn if n is odd and Kn less a one-factor if n is even. In this paper it is shown that, for non-negative integers p, q and r, there is a decomposition of G into p 4-cycles, q 6-cycles and r 8-cycles if 4p+6q+8r = |E(G)|, q = 0 if n < 6 and r = 0 if n < 8.

This paper concerns graph embedding under topological constraints. We address the problem of nding a planar embedding of a graph satisfying a set of constraints between its vertices and cycles that require embedding a given vertex inside its corresponding cycle. This problem turns out to be NP-complete. However, towards an analysis of its tractable subproblems, we develop an eecient algorithm f...

Graph dynamical systems (GDSs) generalize concepts such as cellular automata and Boolean networks and can describe a wide range of distributed, nonlinear phenomena. Two GDSs are cycle equivalent if their periodic orbits are isomorphic as directed graphs, which captures the notion of having comparable long-term dynamics. In this paper, we study cycle equivalence of GDSs in which the vertex funct...

A cycle C is a vertex-dominating cycle if every vertex is adjacent to some vertex of C. Bondy and Fan [4] showed that if G is a 2-connected graph with δ(G) ≥ 13 (|V (G)| − 4), then G has a vertex-dominating cycle. In this paper, we prove that if G is a 2-connected bipartite graph with partite sets V1 and V2 such that δ(G) ≥ 1 3 (max{|V1|, |V2|}+ 1), then G has a vertex-dominating cycle.