共查询到20条相似文献,搜索用时 15 毫秒
1.
Richard Hammack Wilfried Imrich Sandi Klavžar 《Journal of Algebraic Combinatorics》2016,43(4):837-850
This paper concerns finite, edge-transitive direct and strong products, as well as infinite weak Cartesian products. We prove that the direct product of two connected, non-bipartite graphs is edge-transitive if and only if both factors are edge-transitive and at least one is arc-transitive, or one factor is edge-transitive and the other is a complete graph with loops at each vertex. Also, a strong product is edge-transitive if and only if all factors are complete graphs. In addition, a connected, infinite non-trivial Cartesian product graph G is edge-transitive if and only if it is vertex-transitive and if G is a finite weak Cartesian power of a connected, edge- and vertex-transitive graph H, or if G is the weak Cartesian power of a connected, bipartite, edge-transitive graph H that is not vertex-transitive. 相似文献
2.
Boštjan Brešar 《Discrete Mathematics》2008,308(23):5555-5561
A set S of vertices of a graph G is a geodetic set if every vertex of G lies in at least one interval between the vertices of S. The size of a minimum geodetic set in G is the geodetic number of G. Upper bounds for the geodetic number of Cartesian product graphs are proved and for several classes exact values are obtained. It is proved that many metrically defined sets in Cartesian products have product structure and that the contour set of a Cartesian product is geodetic if and only if their projections are geodetic sets in factors. 相似文献
3.
An identifying code of a (di)graph G is a dominating subset C of the vertices of G such that all distinct vertices of G have distinct (in)neighbourhoods within C. In this paper, we classify all finite digraphs which only admit their whole vertex set as an identifying code. We also classify all such infinite oriented graphs. Furthermore, by relating this concept to a well-known theorem of Bondy on set systems, we classify the extremal cases for this theorem. 相似文献
4.
Marc Chastand 《Discrete Mathematics》2006,306(13):1272-1284
We prove that the non-trivial (finite or infinite) weakly median graphs which are undecomposable with respect to gated amalgamation and Cartesian multiplication are the 5-wheels, the subhyperoctahedra different from K1, the path K1,2 and the 4-cycle K2,2, and the two-connected K4- and K1,1,3-free bridged graphs. These prime graphs are exactly the weakly median graphs which do not have any proper gated subgraphs other than singletons. For finite graphs, these results were already proved in [H.-J. Bandelt, V.C. Chepoi, The algebra of metric betweenness I: subdirect representation, retracts, and axiomatics of weakly median graphs, preprint, 2002]. A graph G is said to have the half-space copoint property (HSCP) if every non-trivial half-space of the geodesic convexity of G is a copoint at each of its neighbors. It turns out that any median graph has the HSCP. We characterize the weakly median graphs having the HSCP. We prove that the class of these graphs is closed under gated amalgamation and Cartesian multiplication, and we describe the prime and the finite regular elements of this class. 相似文献
5.
Amitabha Tripathi 《Discrete Applied Mathematics》2007,155(5):670-671
For a finite simple graph G, we denote the set of degrees of its vertices, known as its degree set, by D(G). Kapoor, Polimeni and Wall [Degree sets for graphs, Fund. Math. 95 (1977) 189-194] have determined the least number of vertices among graphs with a given degree set. We give a very short proof of this result. 相似文献
6.
On bipartite zero-divisor graphs 总被引:1,自引:0,他引:1
A (finite or infinite) complete bipartite graph together with some end vertices all adjacent to a common vertex is called a complete bipartite graph with a horn. For any bipartite graph G, we show that G is the graph of a commutative semigroup with 0 if and only if it is one of the following graphs: star graph, two-star graph, complete bipartite graph, complete bipartite graph with a horn. We also prove that a zero-divisor graph is bipartite if and only if it contains no triangles. In addition, we give all corresponding zero-divisor semigroups of a class of complete bipartite graphs with a horn and determine which complete r-partite graphs with a horn have a corresponding semigroup for r≥3. 相似文献
7.
Given an initial graph G, one may apply a rule R to G which replaces certain vertices of G with other graphs called replacement graphs to obtain a new graph R(G). By iterating this procedure, a sequence of graphs {Rn(G)} is obtained. When each graph in this sequence is normalized to have diameter one, the resulting sequence may converge in the Gromov-Hausdorff metric. In this paper, we compute the topological dimension of limit spaces of normalized sequences of iterated vertex replacements involving more than one replacement graph. We also give examples of vertex replacement rules that yield fractals. 相似文献
8.
We show that regular median graphs of linear growth are the Cartesian product of finite hypercubes with the two-way infinite path. Such graphs are Cayley graphs and have only two ends.For cubic median graphs G the condition of linear growth can be weakened to the condition that G has two ends. For higher degree the relaxation to two-ended graphs is not possible, which we demonstrate by an example of a median graph of degree four that has two ends, but nonlinear growth. 相似文献
9.
Thomas Andreae 《Journal of Combinatorial Theory, Series B》1982,33(2):178-186
For each positive integer n, let Tn be the tree in which exactly one vertex has degree n and all the other vertices have degree n + 1. A graph G is called stable if its edge set is nonempty and if deleting an arbitrary edge of G there is always a component of the residue graph which is isomorphic to G. The question whether there are locally finite stable graphs that are not isomorphic to one of the graphs Tn is answered affirmatively by constructing an uncountable family of pairwise nonisomorphic, locally finite, stable graphs. Further, the following results are proved: (1) Among the locally finite trees containing no subdivision of T2, the oneway infinite path T1 is the only stable graph. (2) Among the locally finite graphs containing no two-way infinite path, T1 is also the only stable graph. 相似文献
10.
Gabriel A. Barragán-Ramírez Juan A. Rodríguez-Velázquez 《Graphs and Combinatorics》2016,32(4):1263-1278
A vertex \(v\in V(G)\) is said to distinguish two vertices \(x,y\in V(G)\) of a nontrivial connected graph G if the distance from v to x is different from the distance from v to y. A set \(S\subset V(G)\) is a local metric generator for G if every two adjacent vertices of G are distinguished by some vertex of S. A local metric generator with the minimum cardinality is called a local metric basis for G and its cardinality, the local metric dimension of G. It is known that the problem of computing the local metric dimension of a graph is NP-Complete. In this paper we study the problem of finding exact values or bounds for the local metric dimension of strong product of graphs. 相似文献
11.
Robert F. Bailey 《Annals of Combinatorics》2016,20(4):641-659
A resolving set for a graph \({\Gamma}\) is a collection of vertices S, chosen so that for each vertex v, the list of distances from v to the members of S uniquely specifies v. The metric dimension of \({\Gamma}\) is the smallest size of a resolving set for \({\Gamma}\). Much attention has been paid to the metric dimension of distance-regular graphs. Work of Babai from the early 1980s yields general bounds on the metric dimension of primitive distance-regular graphs in terms of their parameters. We show how the metric dimension of an imprimitive distance-regular graph can be related to that of its halved and folded graphs. We also consider infinite families (including Taylor graphs and the incidence graphs of certain symmetric designs) where more precise results are possible. 相似文献
12.
Ismael González Yero Dorota Kuziak Amauris Rondón Aguilar 《Aequationes Mathematicae》2013,86(1-2):1-21
A vertex coloring of a graph G is an assignment of colors to the vertices of G so that every two adjacent vertices of G have different colors. A coloring related property of a graphs is also an assignment of colors or labels to the vertices of a graph, in which the process of labeling is done according to an extra condition. A set S of vertices of a graph G is a dominating set in G if every vertex outside of S is adjacent to at least one vertex belonging to S. A domination parameter of G is related to those structures of a graph that satisfy some domination property together with other conditions on the vertices of G. In this article we study several mathematical properties related to coloring, domination and location of corona graphs. We investigate the distance-k colorings of corona graphs. Particularly, we obtain tight bounds for the distance-2 chromatic number and distance-3 chromatic number of corona graphs, through some relationships between the distance-k chromatic number of corona graphs and the distance-k chromatic number of its factors. Moreover, we give the exact value of the distance-k chromatic number of the corona of a path and an arbitrary graph. On the other hand, we obtain bounds for the Roman dominating number and the locating–domination number of corona graphs. We give closed formulaes for the k-domination number, the distance-k domination number, the independence domination number, the domatic number and the idomatic number of corona graphs. 相似文献
13.
Erwin Pesch 《Journal of Graph Theory》1987,11(4):585-598
A graph H is an absolute retract if for every isometric embedding h of, into a graph G an edge-preserving map g from G to H exists such that g · h is the identity map on H. A vertex v is embeddable in a graph G if G ? v is a retract of G. An absolute retract is uniquely determined by its set of embeddable vertices. We may regard this set as a metric space. We also prove that a graph (finite metric space with integral distance) can be isometrically embedded into only one smallest absolute retract (injective hull). All graphs in this paper are finite, connected, and without multiple edges. 相似文献
14.
《Discrete Mathematics》2023,346(1):113162
The graph coloring game is a two-player game in which the two players properly color an uncolored vertex of G alternately. The first player wins the game if all vertices of G are colored, and the second wins otherwise. The game chromatic number of a graph G is the minimum integer k such that the first player has a winning strategy for the graph coloring game on G with k colors. There is a lot of literature on the game chromatic number of graph products, e.g., the Cartesian product and the lexicographic product. In this paper, we investigate the game chromatic number of the strong product of graphs, which is one of major graph products. In particular, we completely determine the game chromatic number of the strong product of a double star and a complete graph. Moreover, we estimate the game chromatic number of some King's graphs, which are the strong products of two paths. 相似文献
15.
A graph G is a queens graph if the vertices of G can be mapped to queens on the chessboard such that two vertices are adjacent if and only if the corresponding queens attack each other, i.e. they are in horizontal, vertical or diagonal position.We prove a conjecture of Beineke, Broere and Henning that the Cartesian product of an odd cycle and a path is a queens graph. We show that the same does not hold for two odd cycles. The representation of the Cartesian product of an odd cycle and an even cycle remains an open problem.We also prove constructively that any finite subgraph of the rectangular grid or the hexagonal grid is a queens graph.Using a small computer search we solve another conjecture of the authors mentioned above, saying that K3,4 minus an edge is a minimal non-queens graph. 相似文献
16.
The clique graph of a graph G is the graph obtained by taking the cliques of G as vertices, and two vertices are adjacent if and only if the corresponding cliques have a non-empty intersection. A graph is self-clique if it is isomorphic to its clique graph. We give a new characterization of the set of all connected self-clique graphs having all cliques but two of size 2. 相似文献
17.
Let G be a connected (di)graph. A vertex w is said to strongly resolve a pair u,v of vertices of G if there exists some shortest u-w path containing v or some shortest v-w path containing u. A set W of vertices is a strong resolving set for G if every pair of vertices of G is strongly resolved by some vertex of W. The smallest cardinality of a strong resolving set for G is called the strong dimension of G. It is shown that the problem of finding the strong dimension of a connected graph can be transformed to the problem of finding the vertex covering number of a graph. Moreover, it is shown that computing this invariant is NP-hard. Related invariants for directed graphs are defined and studied. 相似文献
18.
A graph G is traceable if there is a path passing through all the vertices of G. It is proved that every infinite traceable graph either contains arbitrarily large finite chordless paths, or contains a subgraph isomorphic to graph A, illustrated in the text. A corollary is that every finitely generated infinite lattice of length 3 contains arbitrarily large finite fences. It is also proved that every infinite traceable graph containing no chordless four-point path contains a subgraph isomorphic to Kω,ω. The versions of these results for finite graphs are discussed. 相似文献
19.
Carsten Thomassen 《Combinatorica》2016,36(5):601-621
We prove a decomposition result for locally finite graphs which can be used to extend results on edge-connectivity from finite to infinite graphs. It implies that every 4k-edge-connected graph G contains an immersion of some finite 2k-edge-connected Eulerian graph containing any prescribed vertex set (while planar graphs show that G need not containa subdivision of a simple finite graph of large edge-connectivity). Also, every 8k-edge connected infinite graph has a k-arc-connected orientation, as conjectured in 1989. 相似文献
20.
A graph G is loosely-c-connected, or ?-c-connected, if there exists a number d depending on G such that the deletion of fewer than c vertices from G leaves precisely one infinite component and a graph containing at most d vertices. In this paper, we give the structure of a set of ?-c-connected infinite graphs that form an unavoidable set among the topological minors of ?-c-connected infinite graphs. Corresponding results for minors and parallel minors are also obtained. 相似文献