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We show that the probability for a finitely generated subgroup of the modular group, of size $n$, to be almost malnormal or non-parabolic, tends to 0 as $n$ tends to infinity -- where the notion of the size of a subgroup is based on a…

Group Theory · Mathematics 2023-11-15 Frédérique Bassino , Cyril Nicaud , Pascal Weil

The motion of a graph is the minimal degree of its full automorphism group. Babai conjectured that the motion of a primitive distance-regular graph on $n$ vertices of diameter greater than two is at least $n/C$ for some universal constant…

Combinatorics · Mathematics 2023-12-04 László Pyber , Saveliy V. Skresanov

We derive attainable upper bounds on the algebraic connectivity (spectral gap) of a regular graph in terms of its diameter and girth. This bound agrees with the well-known Alon-Boppana-Friedman bound for graphs of even diameter, but is an…

Combinatorics · Mathematics 2023-07-17 Geoffrey Exoo , Theodore Kolokolnikov , Jeanette Janssen , Timothy Salamon

We generalize the asymptotic behavior of the graph distance between two uniformly chosen nodes in the configuration model to a wide class of random graphs. Among others, this class contains the Poissonian random graph, the expected degree…

Probability · Mathematics 2008-05-19 Henri van den Esker , Remco van der Hofstad , Gerard Hooghiemstra

In this paper, we exploit the theory of dense graph limits to provide a new framework to study the stability of graph partitioning methods, which we call structural consistency. Both stability under perturbation as well as asymptotic…

Combinatorics · Mathematics 2016-08-15 Peter Diao , Dominique Guillot , Apoorva Khare , Bala Rajaratnam

An algorithmic upper bound on the domination number $\gamma$ of graphs in terms of the order $n$ and the minimum degree $\delta$ is proved. It is demonstrated that the bound improves best previous bounds for any $5\le \delta \le 50$. In…

Combinatorics · Mathematics 2014-10-17 Csilla Bujtás , Sandi Klavžar

Current modularity-based community detection algorithms attempt to find cluster memberships that maximize modularity within a fixed graph topology. Diverging from this conventional approach, our work introduces a novel strategy that employs…

Data Analysis, Statistics and Probability · Physics 2024-02-27 Yongyu Wang , Shiqi Hao , Xiaoyang Wang , Xiaotian Zhuang

In this paper, we study the order of a maximal clique in an amply regular graph with a fixed smallest eigenvalue by considering a vertex that is adjacent to some (but not all) vertices of the maximal clique. As a consequence, we show that…

Combinatorics · Mathematics 2020-12-18 Gary R. W. Greaves , Jack H. Koolen , Jongyook Park

We have analyzed the detectability limits of network communities in the framework of the popular Girvan and Newman benchmark. By carefully taking into account the inevitable stochastic fluctuations that affect the construction of each and…

Physics and Society · Physics 2013-12-16 Lucio Floretta , Jonas Liechti , Alessandro Flammini , Paolo De Los Rios

We give a linear-time algorithm that approximately uniformly generates a random simple graph with a power-law degree sequence whose exponent is at least 2.8811. While sampling graphs with power-law degree sequence of exponent at least 3 is…

Combinatorics · Mathematics 2017-11-15 Pu Gao , Nicholas Wormald

We study the preferential attachment model $G_n^h$. A graph $G_n^h$ is generated from a finite initial graph by adding new vertices one at a time. Each new vertex connects to $h\ge 1$ already existing vertices, and these are chosen with…

Probability · Mathematics 2026-01-12 Katarzyna Rybarczyk , Małgorzata Sulkowska

A class A of labelled graphs is bridge-addable if for all graphs G in A and all vertices u and v in distinct connected components of G, the graph obtained by adding an edge between u and u is also in A; the class A is monotone if for all G…

Combinatorics · Mathematics 2011-10-04 Louigi Addario Berry , Colin McDiarmid , Bruce Reed

We prove that the class of chordal graphs is easily testable in the following sense. There exists a constant $c>0$ such that, if adding/removing at most $\epsilon n^2$ edges to a graph $G$ with $n$ vertices does not make it chordal, then a…

Combinatorics · Mathematics 2019-02-19 Rémi de Joannis de Verclos

Nodes in real-world networks are repeatedly observed to form dense clusters, often referred to as communities. Methods to detect these groups of nodes usually maximize an objective function, which implicitly contains the definition of a…

Physics and Society · Physics 2015-09-10 V. A. Traag , R. Aldecoa , J-C. Delvenne

The maximum likelihood threshold (MLT) of a graph $G$ is the minimum number of samples to almost surely guarantee existence of the maximum likelihood estimate in the corresponding Gaussian graphical model. We give a new characterization of…

We study the richness of the ensemble of graphical structures (i.e., unlabeled graphs) of the one-dimensional random geometric graph model defined by $n$ nodes randomly scattered in $[0,1]$ that connect if they are within the connection…

Information Theory · Computer Science 2022-06-24 Mihai-Alin Badiu , Justin P. Coon

We bound the second eigenvalue of random $d$-regular graphs, for a wide range of degrees $d$, using a novel approach based on Fourier analysis. Let $G_{n, d}$ be a uniform random $d$-regular graph on $n$ vertices, and let $\lambda (G_{n,…

Combinatorics · Mathematics 2022-12-06 Amir Sarid

We exploit a result by Nerman which shows that conditional limit theorems hold when a certain monotonicity condition is satisfied. Our main result is an application to vertex degrees in random graphs, where we obtain asymptotic normality…

Probability · Mathematics 2009-09-29 Svante Janson

We give variants of the Krein bound and the absolute bound for graphs with a spectrum similar to that of a strongly regular graph. In particular, we investigate what we call approximately strongly regular graphs. We apply our results to…

Combinatorics · Mathematics 2022-08-10 Ferdinand Ihringer

A $1$-factorization of a graph $G$ is a collection of edge-disjoint perfect matchings whose union is $E(G)$. A trivial necessary condition for $G$ to admit a $1$-factorization is that $|V(G)|$ is even and $G$ is regular; the converse is…

Combinatorics · Mathematics 2018-04-09 Asaf Ferber , Vishesh Jain
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