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We present a new approach to showing that random graphs are nearly optimal expanders. This approach is based on recent deep results in combinatorial group theory. It applies to both regular and irregular random graphs. Let G be a random…

Combinatorics · Mathematics 2015-08-24 Doron Puder

Consider the family of all perfect matchings of the complete graph $K_{2n}$ with $2n$ vertices. Given any collection $\mathcal M$ of perfect matchings of size $s$, there exists a maximum number $f(n,x)$ such that if $s\leq f(n,x)$, then…

Combinatorics · Mathematics 2021-09-30 Cheng Yeaw Ku , Alan J. Aw

We show that every cubic bridgeless graph G has at least 2^(|V(G)|/3656) perfect matchings. This confirms an old conjecture of Lovasz and Plummer. This version of the paper uses a different definition of a burl from the journal version of…

Combinatorics · Mathematics 2015-09-28 Louis Esperet , Frantisek Kardos , Andrew King , Daniel Kral , Serguei Norine

We prove that the `Upper Matching Conjecture' of Friedland, Krop, and Markstr\"om and the analogous conjecture of Kahn for independent sets in regular graphs hold for all large enough graphs as a function of the degree. That is, for every…

Combinatorics · Mathematics 2021-08-02 Ewan Davies , Matthew Jenssen , Will Perkins

In this paper, we generalize the notions of perfect matchings, perfect 2-matchings to perfect k-matchings and give a necessary and sufficient condition for existence of perfect k-matchings. For bipartite graphs, we show that this k-matching…

Combinatorics · Mathematics 2010-08-26 Hongliang Lu

This is a short survey about the theory of stable polynomials and its applications. It gives self-contained proofs of two theorems of Schrijver. One of them asserts that for a $d$--regular bipartite graph $G$ on $2n$ vertices, the number of…

Combinatorics · Mathematics 2021-03-15 Péter Csikvári , Ádám Schweitzer

A matching $M$ of a graph $G$ is maximal if it is not a proper subset of any other matching in $G$. Maximal matchings are much less known and researched than their maximum and perfect counterparts. In particular, almost nothing is known…

Combinatorics · Mathematics 2015-11-03 Tomislav Došlić , Taylor Short

We show that the number of $k$-matching in a given undirected graph $G$ is equal to the number of perfect matching of the corresponding graph $G_k$ on an even number of vertices divided by a suitable factor. If $G$ is bipartite then one can…

Computational Complexity · Computer Science 2016-08-31 Shmuel Friedland , Daniel Levy

We prove that, for positive integers $n,a_1, a_2, a_3$ satisfying $a_1+a_2+a_3 = n-1$, it holds that any bipartite graph $G$ which is the union of three perfect matchings $M_1$, $M_2$, and $M_3$ on $2n$ vertices contains a matching $M$ such…

Combinatorics · Mathematics 2025-07-30 Simona Boyadzhiyska , Micha Christoph , Tibor Szabó

We introduce the concept of matching connectivity as a notion of connectivity in graph admitting perfect matchings which heavily relies on the structural properties of those matchings. We generalise a result of Robertson, Seymour and Thomas…

Combinatorics · Mathematics 2019-02-25 Archontia C. Giannopoulou , Stephan Kreutzer , Sebastian Wiederrecht

In this paper, we introduce a corresponding between bipartite graphs with a perfect matching and digraphs, which implicates an equivalent relation between the extendibility of bipartite graphs and the strongly connectivity of digraphs. Such…

Combinatorics · Mathematics 2010-11-22 Zan-Bo Zhang , Dingjun Lou

Jerrum, Sinclair and Vigoda (2004) showed that the permanent of any square matrix can be estimated in polynomial time. This computation can be viewed as approximating the partition function of edge-weighted matchings in a bipartite graph.…

Discrete Mathematics · Computer Science 2021-06-25 Martin Dyer , Mark Jerrum , Haiko Muller , Kristina Vuskovic

Combining ideas of Pham, Sah, Sawhney, and Simkin on spread perfect matchings in super-regular bipartite graphs with an algorithmic blow-up lemma, we prove a spread version of the blow-up lemma. Intuitively, this means that there exists a…

Combinatorics · Mathematics 2024-10-10 Rajko Nenadov , Huy Tuan Pham

We prove that there exist perfect graphs of arbitrarily large clique-chromatic number. These graphs can be obtained from cobipartite graphs by repeatedly gluing along cliques. This negatively answers a question raised by Duffus, Sands,…

Combinatorics · Mathematics 2023-10-24 Pierre Charbit , Irena Penev , Stéphan Thomassé , Nicolas Trotignon

In this paper, we prove that the 2-factor polynomial, an invariant of a planar trivalent graph with a perfect matching, counts the number of 2- factors that contain the the perfect matching as a subgraph. Consequently, we show that the…

Combinatorics · Mathematics 2020-06-02 Scott Baldridge , Adam M. Lowrance , Ben McCarty

This paper analyzes the performance of sequential importance sampling algorithms for estimating the number of perfect matchings in bipartite graphs. Precise bounds on the number of samples required to yield an accurate estimate are derived.…

Probability · Mathematics 2021-01-01 Andy Tsao

We prove that Broder's Markov chain for approximate sampling near-perfect and perfect matchings is not rapidly mixing for Hamiltonian, regular, threshold and planar bipartite graphs, filling a gap in the literature. In the second part we…

Discrete Mathematics · Computer Science 2014-04-17 Annabell Berger , Steffen Rechner

We give an upper bound on the number of perfect matchings in an undirected simple graph $G$ with an even number of vertices, in terms of the degrees of all the vertices in $G$. This bound is sharp if $G$ is a union of complete bipartite…

Combinatorics · Mathematics 2008-03-07 Shmuel Friedland

Using Je\v{r}\'abek 's framework for probabilistic reasoning, we formalize the correctness of two fundamental RNC^2 algorithms for bipartite perfect matching within the theory VPV for polytime reasoning. The first algorithm is for testing…

Logic in Computer Science · Computer Science 2015-07-01 Dai Tri Man Le , Stephen A. Cook

We give a sharp lower bound on the number of matchings of a given size in a bipartite graph. When specialized to regular bipartite graphs, our results imply Friedland's Lower Matching Conjecture and Schrijver's theorem proven by Gurvits and…

Combinatorics · Mathematics 2015-11-06 Marc Lelarge