关于联图P_1VP_n的k-强优美性

本文研究了联图P_1VP_n的k-强优美性问题.利用K-强优美图的定义,获得了联图P_1VP_n是k-强优美图的必要条件,还得到了当n:2k-1时联图P_1VP_n是k-强优美图,亦是k-优美图,及当n≥3时联图P_1VP_n是2-强优美图,也是2-优美图的结果,推广了联图P_1VP_n是优美图的结果.     

关于分数k-因子临界图与分数k-可扩图的若干结果

一个简单图G, 如果对于V(G)的任意k元子集S, 子图G-S都包含分数完美匹配, 那么称G为分数k-因子临界图. 如果图G的每个k-匹配M都包含在一个分数完美匹配中, 那么称图G为分数k-可扩图. 给出一个图是分数k-因子临界图和分数k-可扩图的充分条件, 并给出一个图是分数k-因子临界图的充分必要条件.     

线团-收敛图

一个图的线团图就是这个图的线图的团图。对于自然数n，一个图被称为n-线团－收敛的，如果它的n次线团图同构于一个固定的图。否则称之为发散的。本刻画了线团－收敛图与发散图，给出一个线团－收敛图的构造方法，并且，讨论了线团－收敛图的线团－收敛指数。     

紧图的两个结果及其应用

双随机矩阵有许多重要的应用, 紧图族可以看作是组合矩阵论中关于双随机矩阵的著名的Birkhoff定理的拓广,具有重要的研究价值． 确定一个图是否紧图是个困难的问题,目前已知的紧图族尚且不多.给出了两个重要结果：任意紧图与任意多个孤立点的不交并是紧图;任意紧图的每一个顶点上各增加一条悬挂边的图是紧图． 利用这两个结果,从已知紧图可构造出无穷多个紧图族．     

Weak Graph Map Homotopy and Its Applications∗

The authors introduce a notion of a weak graph map homotopy (they call it M-homotopy), discuss its properties and applications. They prove that the weak graph map homotopy equivalence between graphs coincides with the graph homotopy equivalence defined by Yau et al in 2001. The difference between them is that the weak graph map homotopy transformation is defined in terms of maps, while the graph homotopy transformation is defined by means of combinatorial operations. They discuss its advantages over the graph homotopy transformation. As its applications, they investigate the mapping class group of a graph and the 1-order MP-homotopy group of a pointed simple graph. Moreover, they show that the 1-order MP-homotopy group of a pointed simple graph is invariant up to the weak graph map homotopy equivalence.     

Efficient Pattern Matching on Graph Patterns of Bounded Treewidth

This paper deals with a problem to decide whether a given graph structure appears as a pattern in the structure of a given graph. A graph pattern is a connected graph with structured variables. A variable is an ordered list of vertices that can be replaced with a connected graph by a kind of hyperedge replacements. The graph pattern matching problem (GPMP) is the computational problem to decide whether a given graph pattern matches a given graph. In this paper, we show that GPMP is solvable in polynomial time if for a given graph pattern p, the lengths of all variables of p are 2 and the base graph of p is of bounded treewidth.     

梯子细分图Ln＊的排斥（下整）和数

（下整）和标号与排斥（下整）和标号是图的一种压缩表示．一个图G称为下整和图,若它同构于某个S Q＋的下整和图．图Pn×K2称为梯子．本文给出了梯子细分图Ln＊的定义,并确定了梯子细分图Ln＊的排斥（下整）和数．     

梯子细分图L_n~*的排斥(下整)和数

(下整)和标号与排斥(下整)和标号是图的一种压缩表示.一个图G称为下整和图,若它同构于某个SQ+的下整和图.图Pn×K2称为梯子.本文给出了梯子细分图Ln*的定义,并确定了梯子细分图Ln*的排斥(下整)和数.     

射影平面上标号图的辅助图

刘彦佩教授给出了平面图的辅助图.推广平面图的辅助图到射影平面,给出标号图的射影平面性的如下刻画:给定标号图$G$对应的辅助图是平衡的当且仅当$G$是射影平面图.     

Connections between generalized graph entropies and graph energy

Dehmer and Mowshowitz introduced a class of generalized graph entropies using known information‐theoretic measures. These measures rely on assigning a probability distribution to a graph. In this article, we prove some extremal properties of such generalized graph entropies by using the graph energy and the spectral moments. Moreover, we study the relationships between the generalized graph entropies and compute the values of the generalized graph entropies for special graph classes. © 2014 Wiley Periodicals, Inc. Complexity 21: 35–41, 2015     

The spectral radii of a graph and its line graph

The spectral radius of a (directed) graph is the largest eigenvalue of adjacency matrix of the (directed) graph. We give the relation on the characteristic polynomials of a directed graph and its line graph, and obtain sharp bounds on the spectral radius of directed graphs. We also give the relation on the spectral radii of a graph and its line graph. As a consequence, the spectral radius of a connected graph does not exceed that of its line graph except that the graph is a path.     

和图、整和图及模和图的几个结果

Let N denote the set of positive integers.The sum graph G (S) of a finite subset S (C) N is the graph (S,E) with uv ∈ E if and only if u v ∈ S.A graph G is said to be a sum graph if it is isomorphic to the sum graph of some S С N.By using the set Z of all integers instead of N,we obtain the definition of the integral sum graph.A graph G=(V,E) is a mod sum graph if there exists a positive integer z and a labelling,λ,of the vertices of G with distinct elements from {0,1,2,...,z-1} so that uv ∈ E if and only if the sum,modulo z,of the labels assigned to u and v is the label of a vertex of G.In this paper,we prove that flower tree is integral sum graph.We prove that Dutch m-wind-mill (Dm) is integral sum graph and mod sum graph,and give the sum number of Dm.     

On permutation graphs

We give an upper bound of the number of edges of a permutation graph. We introduce some necessary conditions for a graph to be a permutation graph, and we discuss the independence of these necessary conditions. We show that they are altogether not sufficient for a graph to be a permutation graph.     

3-连通3-正则图中的可序子集

图G的k元点集X={x1,x2,…,xk}被称为G的k-可序子集,如果X的任意排列都按序排在G的某个圈上.称G是k-可序图,如果G的每一个k元子集都是G的k-可序子集.称G为k-可序Hamilton图,如果X的任意排列都位于G的Hamilton圈上.研究了3-连通3-正则图的可序子集的存在性问题.     

Edge-clique graphs

The edge-clique graphK(G) of a graphG is that graph whose vertices correspond to the edges ofG and where two vertices ofK(G) are adjacent whenever the corresponding edges ofG belong to a common clique. It is shown that every edge-clique graph is a clique graph, and that ifG is either an interval graph or a line graph, then so too isK(G). An algorithm is provided for determining whether a graph is an edge-clique graph. A new graph called the STP graph is introduced and a relationship involving this graph, the edge-clique graph, and the line graph is presented. The STP graphs are also characterized.Research supported in part by Office of Naval Research Contract N00014-88-K-0018.Research supported in part by Office of Naval Research Contract N00014-88-K-0163.     

Every connected regular graph of even degree is a Schreier coset graph

Using Petersen's theorem, that every regular graph of even degree is 2-factorable, it is proved that every connected regular graph of even degree is isomorphic to a Schreier coset graph. The method used is a special application of the permutation voltage graph construction developed by the author and Tucker. This work is related to graph imbedding theory, because a Schreier coset graph is a covering space of a bouquet of circles.     

On bipartite zero-divisor graphs

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.     

Eulerian detachments with local edge-connectivity

For a graph G, a detachment operation at a vertex transforms the graph into a new graph by splitting the vertex into several vertices in such a way that the original graph can be obtained by contracting all the split vertices into a single vertex. A graph obtained from a given graph G by applying detachment operations at several vertices is called a detachment of graph G. While detachment operations may decrease the connectivity of graphs, there are several works on conditions for preserving the connectivity. In this paper, we present necessary and sufficient conditions for a given graph/digraph to have an Eulerian detachment that satisfies a given local edge-connectivity requirement. We also discuss conditions for the detachment to be loopless.     

和图、整和图与模和图的几个结果

Let N denote the set of positive integers. The sum graph G^＋（S） of a finite subset S belong to N is the graph （S, E） with uv ∈ E if and only if u ＋ v ∈ S. A graph G is said to be a sum graph if it is isomorphic to the sum graph of some S belong to N. By using the set Z of all integers instead of N, we obtain the definition of the integral sum graph. A graph G = （V, E） is a mod sum graph if there exists a positive integer z and a labelling, λ, of the vertices of G with distinct elements from {0, 1, 2,..., z - 1} so that uv ∈ E if and only if the sum, modulo z, of the labels assigned to u and v is the label of a vertex of G. In this paper, we prove that flower tree is integral sum graph. We prove that Dutch m-wind-mill （Dm） is integral sum graph and mod sum graph, and give the sum number of Dm.     

最大匹配图的围长

将一个图的所有最大匹配作为顶点集,称两个最大匹配相邻,若它们之一通过交换一条边得到另一个,由引所得图为该图的最大匹配图。本文研究了最大匹配图的围长,从而给出了最大匹配图是树或完全图的条件。