Kirchhoff index of composite graphs

AbstractLet G1+G2, G1∘G2 and G1{G2} be the join, corona and cluster of graphs G1 and G2, respectively. In this paper, Kirchhoff index formulae of these composite graphs are given

Intersection Graphs in Simultaneous Embedding with Fixed Edges

We examine the simultaneous embedding with fixed edges problem for two planar graphs G1 and G2 with the focus on their in- tersection S := G1 ∩ G2 . In particular, we will present the complete set of intersection graphs S that guarantee a simultaneous embedding with fixed edges for (G1 , G2 ). More formally, we define the subset ISEFE of all planar graphs as follows: A graph S lies in ISEFE if every pair of pla- nar graphs (G1 , G2 ) with intersection S = G1 ∩ G2 has a simultaneous embedding with fixed edges. We will characterize this set by a detailed study of topological embeddings and finally give a complete list of graphs in this set as our main result of this paper

Intersection Graphs in Simultaneous Embedding with Fixed Edges

We examine the simultaneous embedding with ?xed edges problem for two planar graphs G1 and G2 with the focus on their in- tersection S := G1 ? G2 . In particular, we will present the complete set of intersection graphs S that guarantee a simultaneous embedding with ?xed edges for (G1 , G2 ). More formally, we de?ne the subset ISEFE of all planar graphs as follows: A graph S lies in ISEFE if every pair of pla- nar graphs (G1 , G2 ) with intersection S = G1 ? G2 has a simultaneous embedding with ?xed edges. We will characterize this set by a detailed study of topological embeddings and ?nally give a complete list of graphs in this set as our main result of this paper

Matching Domination of Lexicograph Product of Two Graphs

The paper concentrates on the theory of domination in graphs. In this paper we define a new parameter on domination called matching domination set, matching domination number and we have investigated some properties on matching domination of Lexicograph product of two graphs. The following are the results: ? NG(ui, vj ) = {NG1 (ui)XV2} ? {(ui)XNG2 (vj )} ? degG(ui, vj ) =| NG1 (u1) || V2 | ? | NG2 (vj ) ? degG(ui, vj ) = 0 if and only if degG1 (ui) = 0 and degG2 (vj ) = 0 ? If G1, G2 are simple finite graphs without isolated vertices then G1(L)G2 is a finite graph without isolated vertices. ? If G1, G2 are any two graphs without isolated vertices then ?m | G1(L)G2 |= ?m(G1

Parallel critical graphs

Let G1 and G2 be two undirected graphs. Let u1, v1 ∈ V ( G1 ) and u2, v2 ∈ V ( G2 ). A parallel composition forms a new graph H that combines G1 and G2 by contracting the vertices u1 with u2 and v1 with v2. A new kind of graph called a parallel critical graph is introduced in this paper. We present the critical property using the domination number of G1 and G2 and provide a necessary and sufficient condition for parallel critical graphs. Few results relating to some class of graphs and parallel composition are discussed in this paper.Publisher's Versio

The Menger number of the strong product of graphs

The xy-Menger number with respect to a given integer ℓ, for every two vertices x, y in a connected graph G, denoted by ζℓ(x, y), is the maximum number of internally disjoint xy-paths whose lengths are at most ℓ in G. The Menger number of G with respect to ℓ is defined as ζℓ(G) = min{ζℓ(x, y) : x, y ∈ V(G)}. In this paper we focus on the Menger number of the strong product G1 G2 of two connected graphs G1 and G2 with at least three vertices. We show that ζℓ(G1 G2) ≥ ζℓ(G1)ζℓ(G2) and furthermore, that ζℓ+2(G1 G2) ≥ ζℓ(G1)ζℓ(G2) + ζℓ(G1) + ζℓ(G2) if both G1 and G2 have girth at least 5. These bounds are best possible, and in particular, we prove that the last inequality is reached when G1 and G2 are maximally connected graphs.Ministerio de Educación y Ciencia MTM2011-28800-C02-02Generalitat de Cataluña 1298 SGR200

A note on intertwines of infinite graphs

We present a construction of two infinite graphs G1, G2 and of an infinite set F of graphs such that F is an antichain with respect to the minor relation and, for every graph G in F, both G1 and G2 are subgraphs of G but no graph obtained from G by deletion or contraction of an edge has both G1 and G2 as minors. These graphs show that the extension to infinite graphs of the intertwining conjecture of Lovász, Milgram, and Ungar fails. © 1993 Academic Press, Inc

The Hosoya polynomial decomposition for catacondensed benzenoid graphs

AbstractFor a graph G with the vertex set V(G), we denote by d(u,v) the distance between vertices u and v in G, by d(u) the degree of vertex u. The Hosoya polynomial of G is H(G)=∑{u,v}⊆V(G)xd(u,v). The partial Hosoya polynomials of G are Hmn(G)=∑{u,v}⊆V(G)d(u)=m,d(v)=nxd(u,v) for positive integer numbers m and n. It is shown that H(G1)−H(G2)=x2(x+1)2(H33(G1)−H33(G2)),H22(G1)−H22(G2)=(x2+x−1)2(H33(G1)−H33(G2)) and H23(G1)−H23(G2)=2(x2+x−1)(H33(G1)−H33(G2)) for arbitrary catacondensed benzenoid graphs G1 and G2 with equal number of hexagons. As an application, we give an affine relationship between H(G) with two other distance-based polynomials constructed by Gutman [I. Gutman, Some relations between distance-based polynomials of trees, Bulletin de l’Académie Serbe des Sciences et des Arts (Cl. Math. Natur.) 131 (2005) 1–7]