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Triangle-free graphs with uniquely restricted maximum matchings and their corresponding greedoids

机译:具有最大限制唯一匹配的无三角形图及其对应的贪婪

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A matching M is uniquely restricted in a graph G if its saturated vertices induce a subgraph which has a unique perfect matching, namely M itself [M.C. Golumbic, T. Hirst, M. Lewenstein, Uniquely restricted matchings, Algorithmica 31 (2001) 139-154]. G is a Konig-Egervary graph provided alpha(G) + mu(G) = vertical bar V(G)vertical bar [R.W. Deming, Independence numbers of graphs-an extension of the Konig-Egervary theorem, Discrete Math. 27 (1979) 23-33; F. Sterboul, A characterization of the graphs in which the transversal number equals the matching number, J. Combin. Theory Ser. B 27 (1979) 228-229], where mu(G) is the size of a maximum matching and alpha(G) is the cardinality of a maximum stable set. S is a local maximum stable set of G, and we write S epsilon Psi(G), if S is a maximum stable set of the subgraph spanned by S boolean OR N(S), where N(S) is the neighborhood of S. Nernhauser and Trotter [Vertex packings: structural properties and algorithms, Math. Programming 8 (1975) 232-248], proved that any S epsilon Psi(G) is a subset of a maximum stable set of G. In [V.E. Levit, E. Mandrescu, Local maximum stable sets in bipartite graphs with uniquely restricted maximum matchings, Discrete Appl. Math. 132 (2003) 163-174] we have proved that for a bipartite graph G, Psi(G) is a greedoid on its vertex set if and only if all its maximum matchings are uniquely restricted. In this paper we demonstrate that if G is a triangle-free graph, then Psi(G) is a greedoid if and only if all its maximum matchings are uniquely restricted and for any S epsilon psi(G), the subgraph spanned by S boolean OR N(S) is a Konig-Egervary graph. (c) 2007 Elsevier B.V. All rights reserved.
机译:如果匹配M的饱和顶点诱导出具有唯一完美匹配的子图,即M本身,则匹配M在图G中被唯一地限制。 Golumbic,T。Hirst,M。Lewenstein,唯一受限匹配,Algorithica 31(2001)139-154]。 G是Konig-Egervary图,它提供alpha(G)+ mu(G)=竖线V(G)竖线[R.W. Deming,图的独立数-Konig-Egervary定理“离散数学”的扩展。 27(1979)23-33; F. Sterboul,图的特征,其中横数等于匹配数,J。Combin。理论系列B 27(1979)228-229],其中mu(G)是最大匹配的大小,而alpha(G)是最大稳定集的基数。 S是G的局部最大稳定集,如果S是由S布尔OR N(S)跨越的子图的最大稳定集,则我们写出S epsilon Psi(G),其中N(S)是S的邻域Nernhauser和Trotter [顶点填充:结构特性和算法,数学程序8(1975)232-248]证明,任何SεPsi(G)都是G的最大稳定集的子集。 Levit,E。Mandrescu,二分图中具有唯一限制的最大匹配的局部最大稳定集,离散应用。数学。 132(2003)163-174]我们证明,对于二部图G,当且仅当其所有最大匹配都受到唯一限制时,Psi(G)才是其顶点集上的贪婪。在本文中,我们证明,如果G是无三角形的图,则Psi(G)是greeedoid且仅当其所有最大匹配都受到唯一限制且对于任何S epsilon psi(G)时,子图都由S布尔值覆盖OR N(S)是Konig-Egervary图。 (c)2007 Elsevier B.V.保留所有权利。

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