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Given any graph $G$, the (adjacency) spread of $G$ is the maximum absolute difference between any two eigenvalues of the adjacency matrix of $G$. In this paper, we resolve a pair of 20-year-old conjectures of Gregory, Hershkowitz, and…

Combinatorics · Mathematics 2021-09-08 Jane Breen , Alex W. N. Riasanovsky , Michael Tait , John Urschel

Using flag algebras, we prove that the minimum density of $8$-cliques in a large graph without an independent set of size $3$ is $491411/268435456+o(1)$, thus resolving a new case of an old problem of Erd\H{o}s [Magyar Tud. Akad. Mat.…

Combinatorics · Mathematics 2026-02-25 Levente Bodnár , Oleg Pikhurko

A $d$-regular graph on $n$ nodes has at most $T_{\max} = \frac{n}{3} \tbinom{d}{2}$ triangles. We compute the leading asymptotics of the probability that a large random $d$-regular graph has at least $c \cdot T_{\max}$ triangles, and…

Combinatorics · Mathematics 2021-04-16 Pim van der Hoorn , Gabor Lippner , Elchanan Mossel

The edge clique cover number $ecc(G)$ of a graph $G$ is the size of the smallest set of complete subgraphs whose union covers all edges of $G$. It has been conjectured that all the simple graphs with independence number two satisfy…

Combinatorics · Mathematics 2021-12-09 Frank Ramamonjisoa

In 2023, Gollin, Hendrey, Methuku, Tompkins and Zhang determined the maximum number of cliques in general 1-planar graphs with order $n$. Their extremal examples have connectivity at most three, except for a few small orders. At the…

Combinatorics · Mathematics 2026-05-08 Yuanqiu Huang , Licheng Zhang

The famous Erd\H{o}s-Rademacher problem asks for the smallest number of $r$-cliques in a graph with the given number of vertices and edges. Despite decades of active attempts, the asymptotic value of this extremal function for all $r$ was…

Combinatorics · Mathematics 2020-12-29 Jaehoon Kim , Hong Liu , Oleg Pikhurko , Maryam Sharifzadeh

Let ccl(G) denote the order of the largest complete minor in a graph G (also called the contraction clique number) and let G(n,p) denote a random graph on n vertices with edge probability p. Bollobas, Catlin and Erdos asymptotically…

Combinatorics · Mathematics 2007-05-23 N. Fountoulakis , D. Kühn , D. Osthus

We study maximal cliques in the collinearity graphs of Desarguesian nets, give some structural results and some numerical information. In particular, we show for Desarguesian nets that the set consisting of a point $x$ together with all its…

Combinatorics · Mathematics 2026-04-28 Andries E. Brouwer , Sergey Goryainov , Leonid Shalaginov , Chi Hoi Yip

It takes $n^2/4$ cliques to cover all the edges of a complete bipartite graph $K_{n/2,n/2}$, but how many cliques does it take to cover all the edges of a graph $G$ if $G$ has no $K_{t,t}$ induced subgraph? We prove that $O(|G|^{2-1/(2t)})$…

Combinatorics · Mathematics 2022-11-23 Tung Nguyen , Alex Scott , Paul Seymour , Stephan Thomasse

We investigate computational problems involving large weights through the lens of kernelization, which is a framework of polynomial-time preprocessing aimed at compressing the instance size. Our main focus is the weighted Clique problem,…

Data Structures and Algorithms · Computer Science 2021-07-07 Bart M. P. Jansen , Shivesh K. Roy , Michał Włodarczyk

Let $\Gamma(n,k)$ be the set of $2$-connected $n$-vertex graphs containing an edge that is not on any cycle of length at least $k+1.$ Let $g_s(n,k)$ denote the maximum number of $s$-cliques in a graph in $\Gamma(n,k).$ Recently, Ji and Ye…

Combinatorics · Mathematics 2023-09-13 Leilei Zhang

In 1966, Erd\H{o}s, Goodman, and P\'osa proved that $\lfloor n^2/4 \rfloor$ cliques are sufficient to cover all edges in any $n$-vertex graph, with tightness achieved by the balanced complete bipartite graph. This result was generalized by…

Combinatorics · Mathematics 2025-06-13 Yihan Chen , Jialin He , Tianying Xie

Given an integer $k$, deciding whether a graph has a clique of size $k$ is an NP-complete problem. Wilf's inequality provides a spectral bound for the clique number of simple graphs. Wilf's inequality is stated as follows: $\frac{n}{n -…

Discrete Mathematics · Computer Science 2025-04-08 Hareshkumar Jadav , Sreekara Madyastha , Rahul Raut , Ranveer Singh

The Birkhoff polytope $\Omega_n$ is the polytope of doubly stochastic matrices of order $n$. The Birkhoff polytope graph $G(\Omega_n)$ is the skeleton of $\Omega_n$; it is the Cayley graph whose vertex set consists of the elements of the…

Combinatorics · Mathematics 2026-01-13 Zejun Huang , Chi-Kwong Li , Eric Swartz , Nung-Sing Sze

A disk graph is an intersection graph of disks in $\mathbb{R}^2$. Determining the computational complexity of finding a maximum clique in a disk graph is a long-standing open problem. In 1990, Clark, Colbourn, and Johnson gave a…

Computational Geometry · Computer Science 2024-07-17 J. Mark Keil , Debajyoti Mondal

We show that a coupling of non-colliding simple random walkers on the complete graph on $n$ vertices can include at most $n - \log n$ walkers. This improves the only previously known upper bound of $n-2$ due to Angel, Holroyd, Martin,…

Probability · Mathematics 2019-06-26 Erik Bates , Lisa Sauermann

We consider a variant of the planted clique problem where we are allowed unbounded computational time but can only investigate a small part of the graph by adaptive edge queries. We determine (up to logarithmic factors) the number of…

Combinatorics · Mathematics 2020-07-27 Miklós Z. Rácz , Benjamin Schiffer

We show that for an infinitely many natural numbers $k$ there are $k$-uniform hypergraphs which admit a `rescaling phenomenon' as described in [9]. More precisely, let $\mathcal{A}(k,I, n)$ denote the class of $k$-graphs on $n$ vertices in…

Combinatorics · Mathematics 2018-07-09 Tomasz Łuczak , Joanna Polcyn , Christian Reiher

One of the central questions in Ramsey theory asks how small can be the size of the largest clique and independent set in a graph on $N$ vertices. By the celebrated result of Erd\H{o}s from 1947, the random graph on $N$ vertices with edge…

Combinatorics · Mathematics 2021-03-18 Benny Sudakov , István Tomon

We give lower bounds on the size and total size of clique partitions of a graph in terms of its spectral radius and minimum degree, and derive a spectral upper bound for the maximum number of edge-disjoint $t$-cliques. The extremal graphs…

Combinatorics · Mathematics 2021-11-05 Jiang Zhou , Edwin R. van Dam