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Regular and distance-regular characterizations of general graphs are well-known. In particular, the spectral excess theorem states that a connected graph G is distance-regular if and only if its spectral excess (a number that can be…

组合数学 · 数学 2013-09-27 A. Abiad , C. Dalfò , M. A. Fiol

This paper proves limit theorems for the number of monochromatic edges in uniform random colorings of general random graphs. These can be seen as generalizations of the birthday problem (what is the chance that there are two friends with…

概率论 · 数学 2018-02-13 Bhaswar B. Bhattacharya , Persi Diaconis , Sumit Mukherjee

We construct a pair of non-isomorphic, bipartite graphs which are not distinguished by counting the number of homomorphisms to any tree. This answers a question motivated by Atserias et al. (LICS 2021). In order to establish the…

离散数学 · 计算机科学 2025-11-19 Anuj Dawar

A recent result of Condon, Kim, K\"{u}hn and Osthus implies that for any $r\geq (\frac{1}{2}+o(1))n$, an $n$-vertex almost $r$-regular graph $G$ has an approximate decomposition into any collections of $n$-vertex bounded degree trees. In…

组合数学 · 数学 2018-08-28 Jaehoon Kim , Younjin Kim , Hong Liu

Barnette's Conjecture claims that all cubic, 3-connected, planar, bipartite graphs are Hamiltonian. We give a translation of this conjecture into the matching-theoretic setting. This allows us to relax the requirement of planarity to give…

组合数学 · 数学 2022-08-17 Maximilian Gorsky , Raphael Steiner , Sebastian Wiederrecht

We consider the bipartite version of the {\it degree/diameter problem}, namely, given natural numbers $d\ge2$ and $D\ge2$, find the maximum number $\N^b(d,D)$ of vertices in a bipartite graph of maximum degree $d$ and diameter $D$. In this…

组合数学 · 数学 2014-05-06 Ramiro Feria-Puron , Mirka Miller , Guillermo Pineda-Villavicencio

The symmetries of complex molecular structures can be modeled by the {\em topological symmetry group} of the underlying embedded graph. It is therefore important to understand which topological symmetry groups can be realized by particular…

几何拓扑 · 数学 2018-08-14 Kathleen Hake , Blake Mellor , Matthew Pittluck

We first introduce the class of bipartite absolute retracts with respect to tree obstructions with at most $k$ leaves. Then, using the theory of homomorphism duality, we show that this class of absolute retracts coincides exactly with the…

组合数学 · 数学 2016-09-06 Adam Jaffe

We show that for any natural number $s$, there is a constant $\gamma$ and a subgraph-closed class having, for any natural $n$, at most $\gamma^n$ graphs on $n$ vertices up to isomorphism, but no adjacency labeling scheme with labels of size…

We focus in this paper on edge ideals associated to bipartite graphs and give a combinatorial characterization of those having regularity 3. When the regularity is strictly bigger than 3, we determine the first step $i$ in the minimal…

交换代数 · 数学 2012-07-25 Oscar Fernández-Ramos , Philippe Gimenez

Let $k$ be a positive integer and let $G$ be a graph with vertex set $V(G)$. A subset $D \subseteq V(G)$ is a $k$-dominating set if every vertex outside $D$ is adjacent to at least $k$ vertices in $D$. The $k$-domination number…

组合数学 · 数学 2020-05-27 Gülnaz Boruzanlı Ekinci , Csilla Bujtás

The perfect matching problem has a randomized NC algorithm, using the celebrated Isolation Lemma of Mulmuley, Vazirani and Vazirani. The Isolation Lemma states that giving a random weight assignment to the edges of a graph, ensures that it…

计算复杂性 · 计算机科学 2014-12-01 Rahul Arora , Ashu Gupta , Rohit Gurjar , Raghunath Tewari

For a finite group $G$, let $\Delta(G)$ denote the character graph built on the set of degrees of the irreducible complex characters of $G$. In this paper, we show that if the diameter of $\Delta(G)$ is equal to three, then the complement…

群论 · 数学 2019-09-10 Mahdi Ebrahimi

A beautiful conjecture of Erd\H{o}s-Simonovits and Sidorenko states that if H is a bipartite graph, then the random graph with edge density p has in expectation asymptotically the minimum number of copies of H over all graphs of the same…

组合数学 · 数学 2010-06-09 David Conlon , Jacob Fox , Benny Sudakov

We investigate size Ramsey numbers involving bipartite graphs. It is proved that, if each forbidden graph is fixed or grows with n (in a certain uniform manner), then the extremal function has a linear asymptotics. The corresponding slope…

组合数学 · 数学 2007-05-23 Oleg Pikhurko

Consider the binomial model $G^{d+1}(n,p)$ of the random $(d+1)$-uniform hypergraph on $n$ vertices, where each edge is present, independently of one another, with probability $p:\mathbb{N}\to[0,1]$. We prove that, for all…

组合数学 · 数学 2016-02-23 Nicolau C. Saldanha , Márcio Telles

Let \(G\) be a finite group, and let \(\Delta(G)\) denote the \emph{prime graph} built on the set of degrees of the irreducible complex characters of \(G\). It is well known that, whenever \(\Delta(G)\) is connected, the diameter of…

群论 · 数学 2016-07-19 Carlo Casolo , Silvio Dolfi , Emanuele Pacifici , Lucia Sanus

A set S of vertices in a graph G is a dominating set of G if every vertex not in S is adjacent to a vertex in S . The domination number of G, denoted by $\gamma$(G), is the minimum cardinality of a dominating set in G. In a breakthrough…

离散数学 · 计算机科学 2024-10-07 Paul Dorbec , Michael Antony Henning

Cliquewidth is a dense analogue of treewidth. It can be deduced from recent results by Hickingbotham [arXiv:2501.10840] and Nguyen, Scott, and Seymour [arXiv:2501.09839] that graphs of bounded cliquewidth are quasi-isometric to graphs of…

组合数学 · 数学 2025-05-26 Marc Distel

For finite sequence $\underbar{\em d}$ of positive integers, we consider graphs that have $\underbar{\em d}$ as their list of vertex degrees, and bipartite graphs for which each part has $\underbar{\em d}$ as its list of vertex degrees. In…

组合数学 · 数学 2013-03-11 Grant Cairns , Stacey Mendan