共查询到20条相似文献,搜索用时 93 毫秒
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几类图的匹配等价图类 总被引:1,自引:0,他引:1
魏岭 《数学的实践与认识》2011,41(17)
两个图G和H的匹配多项式相等,则称它们匹配等价.用[G]表示图G的所有不同构的匹配等价图的集合.刻画了匹配次大根小于1的图及这些图的补图的匹配等价图类. 相似文献
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黄振杰 《数学的实践与认识》2000,30(4)
一个图 G中含有的三个结点的导出连通子图的个数 S3( G)在网络可靠性中起着重要作用 .在同点数同边数图类中具有最大 S3( G)的图称为 3-优图 ,它所代表的网络是点故障概率接近 1时的最可靠网络 .本文在已有的结果上进一步证明补图为 a K3∪ b K2 ∪ K1和 a K3-x的图分别是各自图类中唯一的 3-优图 ;补图为 a K3∪ ( b-1 ) K2 ∪ 2 K1和 ( a-1 ) K3∪ b K2 ∪ P3的图是该图类中仅有的两个 3-优图 . 相似文献
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对于图G(V,E)的正常k-全染色φ称为G(V,E)的k-均匀全染色,当且仅当任意两个色类中的元素总数至多相差1.xvee(G)=m in{k存在图G的一个k-均匀全染色}称为G的均匀全色数.本文得到了两类M ycielsk i图及圈,轮图和扇形的均匀全色数. 相似文献
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设 T(n,n)表示 n×n 二部竞赛图。本文证明了:如果 uv 是 T(n,n)的一条弧,蕴含d~-(u) d~ (v)≥n-2≥4,则 T(n,n)是 Hamilton 图,除非 T(n,n)属于两类已被刻划的特殊图类。 相似文献
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在文献[3]中介绍了一个新的图类-P3-支配图.这个图类包含所有的拟无爪图,因此也包含所有的无爪图.在本文中,我们证明了每一个点数至少是3的三角形连通的P3-支配图是哈密尔顿的,但有一个例外图K1,1,3.同时,我们也证明了k-连通的(k≥2)的P3-支配图是哈密尔顿的,如果an(G)≤k,但有两个例外图K1,1,3 and K2,3. 相似文献
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The bubble-sort graph Bn is a bipartite graph. Kikuchi and Araki [Edge-bipancyclicity and edge-fault-tolerant bipancyclicity of bubble-sort graphs. Information Processing Letters, 100, 52- 59 (2006)] have proved that Bn is edge-bipancyclic for n ≥ 5 and Bn-F is bipancyclic when n ≥ 4 and |F | ≤ n-3. In this paper, we improve this result by showing that for any edge set F of Bn with |F | ≤ n-3, every edge of Bn F lies on a cycle of every even length from 6 to n! for n ≥ 5 and every edge of Bn F lies on a cycle of every even length from 8 to n! for n = 4. 相似文献
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Cover-Incomparability Graphs of Posets 总被引:1,自引:1,他引:0
Boštjan Brešar Manoj Changat Sandi Klavžar Matjaž Kovše Joseph Mathews Antony Mathews 《Order》2008,25(4):335-347
Cover-incomparability graphs (C-I graphs, for short) are introduced, whose edge-set is the union of edge-sets of the incomparability
and the cover graph of a poset. Posets whose C-I graphs are chordal (resp. distance-hereditary, Ptolemaic) are characterized
in terms of forbidden isometric subposets, and a general approach for studying C-I graphs is proposed. Several open problems
are also stated. 相似文献
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Equistable graphs are graphs admitting positive weights on vertices such that a subset of vertices is a maximal stable set if and only if it is of total weight 1. Strongly equistable graphs are graphs such that for every and every nonempty subset T of vertices that is not a maximal stable set, there exist positive vertex weights assigning weight 1 to every maximal stable set such that the total weight of T does not equal c . General partition graphs are the intersection graphs of set systems over a finite ground set U such that every maximal stable set of the graph corresponds to a partition of U . General partition graphs are exactly the graphs every edge of which is contained in a strong clique. In 1994, Mahadev, Peled, and Sun proved that every strongly equistable graph is equistable, and conjectured that the converse holds as well. In 2009, Orlin proved that every general partition graph is equistable, and conjectured that the converse holds as well. Orlin's conjecture, if true, would imply the conjecture due to Mahadev, Peled, and Sun. An “intermediate” conjecture, posed by Miklavi? and Milani? in 2011, states that every equistable graph has a strong clique. The above conjectures have been verified for several graph classes. We introduce the notion of equistarable graphs and based on it construct counterexamples to all three conjectures within the class of complements of line graphs of triangle‐free graphs. We also show that not all strongly equistable graphs are general partition. 相似文献
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The pre-coloring extension problem consists, given a graph G and a set of nodes to which some colors are already assigned, in finding a coloring of G with the minimum number of colors which respects the pre-coloring assignment. This can be reduced to the usual coloring problem
on a certain contracted graph. We prove that pre-coloring extension is polynomial for complements of Meyniel graphs. We answer
a question of Hujter and Tuza by showing that “PrExt perfect” graphs are exactly the co-Meyniel graphs, which also generalizes
results of Hujter and Tuza and of Hertz. Moreover we show that, given a co-Meyniel graph, the corresponding contracted graph
belongs to a restricted class of perfect graphs (“co-Artemis” graphs, which are “co-perfectly contractile” graphs), whose
perfectness is easier to establish than the strong perfect graph theorem. However, the polynomiality of our algorithm still
depends on the ellipsoid method for coloring perfect graphs.
C.N.R.S.
Final version received: January, 2007 相似文献
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Chi-Kwong Li 《Linear and Multilinear Algebra》2013,61(7):683-693
The energy of a graph is the sum of the absolute values of the eigenvalues of its adjacency matrix. Two graphs are equienergetic if they have the same energy. We construct infinite families of graphs equienergetic with edge-deleted subgraphs. 相似文献
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J.H. Koolen 《Journal of Algebraic Combinatorics》1992,1(4):353-362
Terwilliger [15] has given the diameter bound d (s – 1)(k – 1) + 1 for distance-regular graphs with girth 2s and valency k. We show that the only distance-regular graphs with even girth which reach this bound are the hypercubes and the doubled Odd graphs. Also we improve this bound for bipartite distance-regular graphs. Weichsel [17] conjectures that the only distance-regular subgraphs of a hypercube are the even polygons, the hypercubes and the doubled Odd graphs and proves this in the case of girth 4. We show that the only distance-regular subgraphs of a hypercube with girth 6 are the doubled Odd graphs. If the girth is equal to 8, then its valency is at most 12. 相似文献