In the graph searching game the opponents are a set of searchers and a fugitive in a graph. The searchers try to capture the fugitive by applying some sequence of moves that include placement, removal, or sliding of a searcher along an edge. The fugitive tries to avoid capture by moving along unguarded paths. The search number of a graph is the minimum number of searchers required to guarantee ...

In this paper we consider the problem of finding the smallest number q such that any graph G of order n admits a decomposition into edge disjoint copies of a fixed graph H and single edges with at most q elements. We solve the case when H is the 5-cycle, the 5-cycle with a chord and any connected non-bipartite non-complete graph of order 4.

We introduce and study the Doubly Balanced Connected graph Partitioning (DBCP) problem: Let G=(V,E) be a connected graph with a weight (supply/demand) function p:V→ {−1,+1} satisfying p(V )= ∑ j∈V p(j)=0. The objective is to partition G into (V1, V2) such that G[V1] and G[V2] are connected, |p(V1)|, |p(V2)|≤cp, and max{ |V1| |V2| , |V2| |V1|}≤cs, for some constants cp and cs. When G is 2-connec...

Let G be a graph of order n. A path P of G is extendible if it can be extended to a longer path from one of its two endvertices, otherwise we say P is non-extendible. Let G be a graph of order n. We show that there exists a threshold number s such that every path of order smaller than s is extendible and there exists a non-extendible path of order t for each t ∈ {s, s+ 1, · · · , n} provided G ...

The toughness of a non-complete graph G is the minimum value of |S| ω(G−S) among all separating vertex sets S ⊂ V (G), where ω(G − S) > 2 is the number of components of G−S. It is well-known that every 3-connected planar graph has toughness greater than 1/2. Related to this property, every 3-connected planar graph has many good substructures, such as a spanning tree with maximum degree three, a...

Let G be a connected non-regular graph with n vertices, maximum degree ∆ and minimum degree δ, and let λ1 be the greatest eigenvalue of the adjacency matrix of G. In this paper, by studying the Perron vector of G, it is shown that type-I-a graphs and type-I-b (resp. type-II-a) graphs with some specified properties are not λ1-extremal graphs. Moreover, for each connected non-regular graph some l...

In 1962, S. L. Hakimi proved necessary and sufficient conditions for a given sequence of positive integers d1, d2, . . . , dn to be the degree sequence of a non–separable graph or that of a connected graph. Our goal in this note is to utilize these results to prove closed formulas for the functions dns(2m) and dc(2m), the number of degree sequences with degree sum 2m representable by non–separa...

A graph G is triangularly connected if for every pair of edges e1, e2 ∈ E(G), G has a sequence of 3-cycles C1, C2, · · · , Cl such that e1 ∈ C1, e2 ∈ Cl and such that E(Ci) ∩ E(Ci+1) 6= ∅, (1 ≤ i ≤ l − 1). In this paper it is shown that every triangularly connected claw-free graph G with |E(G)| ≥ 3 is vertex pancyclic. This implies the former results in [2], [3], [4] and [5] that every connecte...

This paper is concerned with the graph searching game. The search number s(G) of a graph G is the smallest number of searchers required to “clear” G. A search strategy is monotone (m) if no recontamination ever occurs. It is connected (c) if the set of clear edges always forms a connected subgraph. It is internal (i) if the removal of searchers is not allowed. The difficulty of the “connected” ...

For a connected graph H of order at least 3, the H-line graph of a graph is defined as that graph whose vertices are the edges of G and where two vertices are adjacent if and only if the corresponding edges of G are adjacent and belong to a common copy of H . In particular, when H = P3, the H-line graph HL(G) is the standard line graph L(G) and for any connected graph G on at least three vertic...