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Leray numbers of complexes of graphs with bounded matching number
Journal of Combinatorial Theory Series A ( IF 0.9 ) Pub Date : 2022-03-17 , DOI: 10.1016/j.jcta.2022.105618
Andreas F. Holmsen 1 , Seunghun Lee 2
Affiliation  

Given a graph G on the vertex set V, the non-matching complex of G, denoted by NMk(G), is the family of subgraphs GG whose matching number ν(G) is strictly less than k. As an attempt to extend the result by Linusson, Shareshian and Welker on the homotopy types of NMk(Kn) and NMk(Kr,s) to arbitrary graphs G, we show that (i) NMk(G) is (3k3)-Leray, and (ii) if G is bipartite, then NMk(G) is (2k2)-Leray. This result is obtained by analyzing the homology of the links of non-empty faces of the complex NMk(G), which vanishes in all dimensions d3k4, and all dimensions d2k3 when G is bipartite. As a corollary, we have the following rainbow matching theorem which generalizes a result by Aharoni, Berger, Chudnovsky, Howard and Seymour: Let E1,,E3k2 be non-empty edge subsets of a graph and suppose that ν(EiEj)k for every ij. Then E=Ei has a rainbow matching of size k. Furthermore, the number of edge sets Ei can be reduced to 2k1 when E is the edge set of a bipartite graph.



中文翻译:

有界匹配数的图复数的 Leray 数

给定顶点集V上的图G , G非匹配复数,表示为纳米ķ(G), 是子图族G'G谁的匹配号码ν(G')严格小于k。作为尝试扩展 Linusson、Shareshian 和 Welker 关于同伦类型的结果纳米ķ(ķn)纳米ķ(ķr,s)对于任意图G,我们证明 (i)纳米ķ(G)(3ķ-3)-Leray,并且 (ii) 如果G是二分的,那么纳米ķ(G)(2ķ-2)-勒雷。这个结果是通过分析复合体的非空面链接的同源性得到的纳米ķ(G),在所有维度上消失d3ķ-4, 和所有维度d2ķ-3G是二分的。作为推论,我们有以下彩虹匹配定理,它概括了 Aharoni、Berger、Chudnovsky、Howard 和 Seymour 的结果:1,,3ķ-2是图的非空边子集并假设ν(一世j)ķ对于每个一世j. 然后=一世有大小为k的彩虹匹配。此外,边集的数量一世可以简化为2ķ-1E是二部图的边集时。

更新日期:2022-03-17
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