3连通图的可去边数

设 e是 3连通图 G的一条边 ,如果 G- e是某个 3连通图的剖分 ,则称 e是 G的可去边 .本文给出了 3连通图的可去边数依赖于极大半轮的下界以及达到下界的极图 .     

C2(4,k) 中的强支撑可迹图

设2≤h≤3,l0,k≥0是整数,C_h(l,k)是由h-边连通简单图组成的集合,图G∈C_h(l,k)当且仅当对图G的任意一个二边割或三边割X,图G-X的每个分支都至少有︱V(G)-k︱/l个点.设e=u_1v_1和e'=u_2v_2是图G的两条边.若e≠e',G(e,e')是将图G中的边e=u_1v_1和e'=u_2v_2分别用路u_1v_ev_1和u_2v_e'v_2替换得到的图(其中,v_e,v_e'是不在V(G)中的两个新的点).若e=e',G(e,e')是将图G中的边e=u_1v_1用路u_1v_ev_1替换得到的图,也记作G(e).若对任意的e,e'∈E(G),G(e,e')都有支撑(v_e,v_e')迹,则称图G是强支撑可迹的.作者证明了,若图G∈C_2(4,k)且|V(G)|5k,则要么图G是强支撑可迹图,要么存在e,e'∈E(G),使得G(e,e')可以收缩成一个有限图类F中的图.当k=4时,F被完全确定了.     

关于几乎唯一泛圈图

设G是阶为n的简单Hamilton图．若存在m(3(?)m＜n)使对每个l∈{3,4,…,n} -{m},G恰有一个长为l的圈且不含长为m的圈,则称G是几乎唯一泛圈图,用(?)k表示具有n k条边和恰有1/2(k 1)(k 2)个圈的简单H图的集合,用(?)_k~*表示具有n k条边恰有2~k k个圈的简单外可平面H图的集合,本文确定了(?)_k和(?)_k~*中所有几乎唯一泛圈图,并证明这些图都是简单MCD图,本文还构造了50个含有同胚于K_4的子图的几乎唯一泛圈图,并提出了若干问题和猜想。     

3-连通3-正则图生成树外的可去边

G是3-连通图，e是G中的一条边．若G-e是3-连通图的一个剖分，则称e是3-连通图的可去边．否则，e是G中不可去边．本给出3-连通3-正则图中生成树外可去边的分布情况及数目．     

一类几乎唯一泛圈图

设G是阶为n的简单Hamilton图．若存在m(3(?)m相似文献   

零和Ramsey数R(C_3,Z_3)的下界——(3)

Bialostocki和Dierker给出了古典Ramaey定理下列有趣的推广:设G是一个有m条边的图,整数k≥2,且k|m,Z_k表示k阶循环群。定义R(G,Z_k)表示一个极小整数t,使得对K_t的边的任意Z_k—染色(即一个泛函C:E(K_t)→Z_k),K_t中都存在一个同构于G的子图具有下列性质 sum from e∈E(G) C(e)≡0(mod k)。本文证明R(C_3,Z_3)≥11。     

图的k符号边控制数

设G=(V,E)是一个图,一个函数f:E→{-1,+1},如果对于G中至少k条边e有sum from e'∈N[e]f(e')≥1成立,则称f为图G的一个k符号边控制函数.一个图的k符号边控制数定义为γ_(ks)^/(G)=min{∑_(e∈E(G))f(e)|f为图G的一个k符号边控制函数}.主要给出了一个图G的k符号边控制数γ_(ks)/(G)=min{∑_(e∈E(G))f(e)|f为图G的一个k符号边控制函数}.主要给出了一个图G的k符号边控制数γ_(ks)^/(G)的若干新下限,并确定了路和圈的k符号边控制数.     

一类混合图的结构及其特征空间

主要讨论具有如下性质的一类连通混合图G:其所有非奇异圈恰有一条公共边,且除了该公共边的端点外,任意两个非奇异圈没有其它交点.本文给出了图G的结构性质,建立了其最小特征值λ1(G)(以及相对应的特征向量)与某个简单图的代数连通度(以及Fiedler向量)之间联系,并应用上述联系证明了λ1(■)≤α(G),其中G是由G通过对其所有无向边定向而获得,α(■)为■的代数连通度.     

带松弛条件的图的强边着色

给定两个非负整数s和t,图G的(s,t)-松弛强k边着色可表示为映射c:E(G)→[k],这个映射满足对G中的任意一条边e,颜色c(e)在e的1-邻域中最多出现s次并且在e的2-邻域中最多出现t次.图G的(s,t)-松弛强边着色指数,记作x'(s,t)(G),表示使得图G有(s,t)-松弛强k边着色的最小k值.在图G中...     

点可迁图的限制边连通性

3限制边割是连通图的一个边割, 它将此图分离成阶不小于3的连通分支. 图G的最小3限制边割所含的边数称为此图的3限制边连通度, 记作λ\-3(G). 它以图G的3阶连通点导出 子图的余边界的最小基数ξ_3(G)为上界. 如果λ_3(G)=ξ_3(G), 则称图G是极大3限制边连通的 . 已知在某种程度上,3限制边连通度较大的网络有较好的可靠性. 作者在文中证明: 如果k正则连通点可迁图的 围长至少是5, 那么它是是极大3限制边连通的.     

关于一些图类的L(1,2)-边标号

For a graph G and two positive integers j and k, an m-L(j, k)-edge-labeling of G is an assignment on the edges to the set {0,..., m}, such that adjacent edges receive labels differing by at least j, and edges which are distance two apart receive labels differing by at least k. The λ′j,k-number of G is the minimum m of an m-L(j, k)-edge-labeling admitted by G.In this article, we study the L(1, 2)-edge-labeling for paths, cycles, complete graphs, complete multipartite graphs, infinite ?-regular trees and wheels.     

On Non-Essential Edges in 3-Connected Graphs

 An edge e in a simple 3-connected graph is deletable (simple-contractible) if the deletion G\e (contraction G/e) is both simple and 3-connected. Suppose a, b, and c are three non-negative integers. If there exists a simple 3-connected graph with exactly a edges which are deletable but not simple-contractible, exactly b edges which are simple-contractible but not deletable, and exactly c edges which are both deletable and simple-contractible, then we call the triple (a, b, c) realizable, and such a graph is said to be an (a, b, c)-graph. Tutte's Wheels Theorem says the only (0, 0, 0)-graphs are the wheels. In this paper, we characterize the (a, b, c) realizable triples for which at least one of a + b≤2, c=0, and c≥16 holds. Received: February 12, 1997 Revised: February 13, 1998     

最大度与最小度相差不超过2的图的平衡judicious划分

图G的顶点集V(G)的一个二部划分V_1和V_2叫做平衡二部划分,如果||V_1|-|V_2||≤1成立.Bollobas和Scott猜想:每一个有m条边且最小度不小于2的图,都存在一个平衡二部划分V_1,V_2,使得max{e(V_1),e(V_2)}≤m/3,此处e(V_i)表示两顶点都在V_i(i=1,2)中的边的条数.他们证明了这个猜想对正则图(即△(G)=δ(G))成立.颜娟和许宝刚证明了每个(k,k-1)-双正则图(即△(G)-δ(G)≤1)存在一个平衡二部划分V_1,V_2,使得每一顶点集的导出子图包含大约m/4条边.这里把该结论推广到最大度和最小度相差不超过2的图G.     

不含某些子图的k连通图中的k可收缩边

最近Ando等证明了在一个$k$($k\geq 5$ 是一个整数) 连通图 $G$ 中,如果 $\delta(G)\geq k+1$, 并且 $G$ 中既不含 $K^{-}_{5}$,也不含 $5K_{1}+P_{3}$, 则$G$ 中含有一条 $k$ 可收缩边.对此进行了推广,证明了在一个$k$连通图$G$中,如果 $\delta(G)\geq k+1$,并且 $G$ 中既不含$K_{2}+(\lfloor\frac{k-1}{2}\rfloor K_{1}\cup P_{3})$,也不含 $tK_{1}+P_{3}$ ($k,t$都是整数,且$t\geq 3$),则当 $k\geq 4t-7$ 时, $G$ 中含有一条 $k$ 可收缩边.     

图的距离无符号拉普拉斯谱半径的关于色数的下界

Let G be a connected graph on n vertices with chromatic number k, and let ρ(G)be the distance signless Laplacian spectral radius of G. We show that ρ(G) ≥ 2n + 2「n k」- 4,with equality if and only if G is a regular Tur′an graph.     

不含相邻三角形的平面图的无圈边着色

An acyclic edge coloring of a graph G is a proper edge coloring such that there are no bichromatic cycles.The acyclic edge chromatic number of a graph G is the minimum number k such that there exists an acyclic edge coloring using k colors and is denoted by χ’ a(G).In this paper we prove that χ ’ a(G) ≤(G) + 5 for planar graphs G without adjacent triangles.     

图的上可嵌入性与独立顶点的新度和

Let G be a k(k ≤3)-edge connected simple graph with minimal degree ≥ 3,girth g,r=g12.For any independent set {a1,a2 , . . . , a 6/(4 k)} of G,if,then G is up-embeddable.     

图的平面Turán数和平面anti-Ramsey数

在所有顶点数为$n$且不包含图$G$作为子图的平面图中,具有最多边数的图的边数称为图$G$的平面Turán数,记为$ex_{_\mathcal{P}}（n,G）$。给定正整数$n$以及平面图$H$,用$\mathcal{T}_n （H）$来表示所有顶点数为$n$且不包含$H$作为子图的平面三角剖分图所组成的图集合。设图集合$\mathcal{T}_n （H）$中的任意平面三角剖分图的任意$k$边染色都不包含彩虹子图$H$,则称满足上述条件的$k$的最大值为图$H$的平面anti-Ramsey数,记作$ar_{_\mathcal{P}}（n,H）$。两类问题的研究均始于2015年左右,至今已经引起了广泛关注。全面地综述两类问题的主要研究成果,以及一些公开问题。     

5连通图中的可去边

An edge e of a k-connected graph G is said to be a removable edge if G O e is still k-connected, where G e denotes the graph obtained from G by deleting e to get G - e, and for any end vertex of e with degree k - 1 in G- e, say x, delete x, and then add edges between any pair of non-adjacent vertices in NG-e （x）. The existence of removable edges of k-connected graphs and some properties of 3-connected and 4-connected graphs have been investigated [1, 11, 14, 15]. In the present paper, we investigate some properties of 5-connected graphs and study the distribution of removable edges on a cycle and a spanning tree in a 5- connected graph. Based on the properties, we proved that for a 5-connected graph G of order at least 10, if the edge-vertex-atom of G contains at least three vertices, then G has at least （3│G│ ＋ 2）/2 removable edges.     

完全图的Cantesian积的L(2,1)-圆标定

For positive integers j and k with j ≥ k, an L（j, k）-labeling of a graph G is an assignment of nonnegative integers to V（G） such that the difference between labels of adjacent vertices is at least j, and the difference between labels of vertices that are distance two apart is at least k. The span of an L（j, k）-labeling of a graph G is the difference between the maximum and minimum integers it uses. The λj, k-number of G is the minimum span taken over all L（j, k）-labelings of G. An m-（j, k）-circular labeling of a graph G is a function f ： V（G） →{0, 1, 2,..., m - 1} such that ｜f（u） - f（v）｜m ≥ j if u and v are adjacent; and ｜f（u） - f（v）｜m 〉 k ifu and v are at distance two, where ｜x｜m = min{｜xl｜, m-｜x｜}. The minimum integer m such that there exists an m-（j, k）-circular labeling of G is called the σj,k-number of G and is denoted by σj,k（G）. This paper determines the σ2,1-number of the Cartesian product of any three complete graphs.