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A new class of isospectral graphs is presented. These graphs are isospectral with respect to both the normalised Laplacian on the discrete graph and the standard differential Laplacian on the corresponding metric graph. The new class of…

Spectral Theory · Mathematics 2023-02-20 Pavel Kurasov , Jacob Muller

In this monography, it is proposed to consider the concepts of spectra of edge cuts and edge cycles of a graph as a basic mathematical structure for solving the problem of graph isomorphism. An edge cut is defined by an edge and the…

Combinatorics · Mathematics 2024-06-13 Sergey Kurapov , Maxim Davidovsky

Szemer\'edi's Regularity Lemma is an important tool for analyzing the structure of dense graphs. There are versions of the Regularity Lemma for sparse graphs, but these only apply when the graph satisfies some local density condition. In…

Combinatorics · Mathematics 2010-11-09 Alexander Scott

In 1999, De Simone and K\"{o}rner conjectured that every graph without induced $C_5,C_7,\overline{C}_7$ contains a clique cover $\mathcal C$ and a stable set cover $\mathcal I$ such that every clique in $\mathcal C$ and every stable set in…

Combinatorics · Mathematics 2015-11-25 Seyed Saeed Changiz Rezaei , Seyyed Aliasghar Hosseini , Bojan Mohar

If $\Gamma$ is a graph for which every edge is in exactly one clique of order $\omega$, then one can form a new graph with vertex set equal to these cliques. This is a generalization of the line graph of $\Gamma$. We discover many general…

Combinatorics · Mathematics 2026-05-25 Connor Phillips

Let $G$ be a graph with $n$ vertices and $\lambda_n(G)$ be the least eigenvalue of its adjacency matrix of $G$. In this paper, we give sharp bounds on the least eigenvalue of graphs without given pathes or cycles and determine the extremal…

Combinatorics · Mathematics 2013-09-27 Mingqing Zhai , Huiqiu Lin , Shicai Gong

We address the problem of identifying a graph structure from the observation of signals defined on its nodes. Fundamentally, the unknown graph encodes direct relationships between signal elements, which we aim to recover from observable…

Social and Information Networks · Computer Science 2016-08-11 Santiago Segarra , Antonio G. Marques , Gonzalo Mateos , Alejandro Ribeiro

We investigate the spectrum of the non-backtracking matrix of a graph. In particular, we show how to obtain eigenvectors of the non-backtracking matrix in terms of eigenvectors of a smaller matrix. Furthermore, we find an expression for the…

Combinatorics · Mathematics 2020-11-19 Cory Glover , Mark Kempton

Graphs that are squares under the gluing algebra arise in the study of homomorphism density inequalities such as Sidorenko's conjecture. Recent work has focused on these homomorphism density applications. This paper takes a new perspective…

Combinatorics · Mathematics 2025-10-08 Karen L. Collins , David Galvin , Christine A. Kelley , Emily McMillon , Amanda Redlich

In a seminal 2005 paper, Haagerup and Thorbj{\o}rnsen discovered that the norm of any noncommutative polynomial of independent complex Gaussian random matrices converges to that of a limiting family of operators that arises from…

Probability · Mathematics 2026-02-12 Ramon van Handel

Let $d\geq 3$ be a fixed integer, and a prime number $p$ such that $\gcd(p,d)=1$. Let $A$ be the adjacency matrix of a random $d$-regular directed graph on $n$ vertices. We show that as a random matrix in ${\mathbb F}_p$, \begin{equation}…

Probability · Mathematics 2019-01-01 Jiaoyang Huang

Let $G$ be a connected graph with adjacency matrix $A(G)$. The distance matrix $D(G)$ of $G$ has rows and columns indexed by $V(G)$ with $uv$-entry equal to the distance $\mathrm{dist}(u,v)$ which is the number of edges in a shortest path…

Combinatorics · Mathematics 2022-12-13 Carlos A. Alfaro , Octavio Zapata

Problems related to graph matching and isomorphisms are very important both from a theoretical and practical perspective, with applications ranging from image and video analysis to biological and biomedical problems. The graph matching…

Combinatorics · Mathematics 2014-09-29 Marcelo Fiori , Guillermo Sapiro

We study regular graphs whose distance-$2$ graph or distance-$1$-or-$2$ graph is strongly regular. We provide a characterization of such graphs $\Gamma$ (among regular graphs with few distinct eigenvalues) in terms of the spectrum and the…

Combinatorics · Mathematics 2019-02-28 C. Dalfó , M. A. Fiol , J. Koolen

We study countable graphs that -- up to isomorphism and with probability one -- arise from a random process, in a similar fashion as the Rado graph. Unlike in the classical case, we do not require that probabilities assigned to pairs of…

Combinatorics · Mathematics 2026-01-23 Ziemowit Kostana , Jarosław Swaczyna , Agnieszka Widz

We use random matrix theory to study the spectrum of random geometric graphs, a fundamental model of spatial networks. Considering ensembles of random geometric graphs we look at short range correlations in the level spacings of the…

Physics and Society · Physics 2017-06-08 Carl P. Dettmann , Orestis Georgiou , Georgie Knight

The standard notion of the Laplacian of a graph is generalized to the setting of a graph with the extra structure of a ``transmission`` system. A transmission system is a mathematical representation of a means of transmitting…

Combinatorics · Mathematics 2009-12-22 Sylvain E. Cappell , Edward Y. Miller

We develop a theory of graph algebras over general fields. This is modeled after the theory developed by Freedman, Lov\'asz and Schrijver in [22] for connection matrices, in the study of graph homomorphism functions over real edge weight…

Discrete Mathematics · Computer Science 2020-07-28 Jin-Yi Cai , Artem Govorov

Generative models for graphs have been typically committed to strong prior assumptions concerning the form of the modeled distributions. Moreover, the vast majority of currently available models are either only suitable for characterizing…

Social and Information Networks · Computer Science 2012-10-19 Antonino Freno , Mikaela Keller , Gemma C. Garriga , Marc Tommasi

We introduce the concept of distance mean-regular graph, which can be seen as a generalization of both vertex-transitive and distance-regular graphs. Let $\Gamma$ be a graph with vertex set $V$, diameter $D$, adjacency matrix $A$, and…

Combinatorics · Mathematics 2015-08-18 V. Diego , M. A. Fiol