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On a perfect matching in a random digraph with average out-degree below two
Journal of Combinatorial Theory Series B ( IF 1.4 ) Pub Date : 2020-03-20 , DOI: 10.1016/j.jctb.2020.03.004
Michal Karoński , Ed Overman , Boris Pittel

Existence of a perfect matching in a random bipartite digraph with bipartition (V1,V2), |Vi|=n, is studied. The graph is generated in two rounds of random selections of a potential matching partner such that the average number of selections made by each vertex overall is below 2. More precisely, in the first round each vertex chooses a potential mate uniformly at random, and independently of all vertices. Given a fixed integer m, a vertex is classified as unpopular if it has been chosen by at most m vertices from the other side. Each unpopular vertex makes yet another uniform/independent selection of a potential mate. The expected number of selections made by a generic vertex v, i.e. its out-degree, is asymptotic to 1+P(Poisson(1)m)(1,2). Aided by Matlab software, we prove that for m=1, whence for all m1, the resulting bipartite graph has a perfect matching a.a.s. (asymptotically almost surely). On the other hand, for m=0 a.a.s. a perfect matching does not exist. For the non-bipartite version of this model with vertex set [n] we show that already for m=0 a.a.s. there exists a partial matching which leaves unmatched a O(log1n) fraction of vertices.



中文翻译:

随机图上的平均匹配度低于2的完美匹配

具有二等分的随机二部有向图的完美匹配的存在 V1个V2|V一世|=ñ,正在研究中。该图是在两轮潜在匹配对象的随机选择中生成的,因此每个顶点总体选择的平均数目低于2。更准确地说,在第一轮中,每个顶点均会随机且独立地均匀选择一个潜在伴侣。所有顶点。给定一个固定的整数m,如果一个顶点最多被另一侧的m个顶点选中,则将其分类为不受欢迎。每个不受欢迎的顶点都会对潜在配偶进行另一个统一/独立的选择。通用顶点v的预期选择次数(即其出学位程度)渐近于1个+P泊松1个1个2。在Matlab软件的帮助下,我们证明了=1个,所有人 1个,生成的二部图具有完美的匹配aas(渐近几乎确定地)。另一方面,对于=0aas不存在完美匹配。对于具有顶点集的该模型的非双向版本[ñ] 我们已经证明了 =0aas存在部分匹配项,从而留下了不匹配的aØ日志-1个ñ 顶点的分数。

更新日期:2020-03-20
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