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On a compact metric graph, we consider the spectrum of the Laplacian defined with a mix of standard and Dirichlet vertex conditions. A Cheeger-type lower bound on the gap $\lambda_2 - \lambda_1$ is established, with a constant that depends…

Spectral Theory · Mathematics 2023-01-19 David Borthwick , Evans M. Harrell , Haozhe Yu

We prove new lower bounds on the likely size of a maximum independent set in a random graph with a given average degree. Our method is a weighted version of the second moment method, where we give each independent set a weight based on the…

Computational Complexity · Computer Science 2011-11-15 Varsha Dani , Cristopher Moore

In this paper we study the maximum value of the largest eigenvalue for simple bipartite graphs, where the number of edges is given and the number of vertices on each side of the bipartition is given. We state a conjectured solution, which…

Combinatorics · Mathematics 2008-09-10 Amitava Bhattacharya , Shmuel Friedland , Uri N. Peled

In 2018, by Ramsey and Hoffman theory, Koolen, Yang, and Yang presented a structural result on graphs with smallest eigenvalue at least $-3$ and large minimum degree. In this study, we depart from the conventional use of Ramsey theory and…

Combinatorics · Mathematics 2025-12-23 Jack H. Koolen , Hong-Jun Ge , Chenhui Lv , Qianqian Yang

The hard-core model can be used to understand the numbers of independent sets in graphs in extremal graph theory. The occupancy fraction, defined as the logarithmic derivative of the independence polynomial of a graph, is a key quantity in…

Combinatorics · Mathematics 2026-04-03 Weiyuan Zhang , Kexiang Xu

We give a survey on graphs with fixed smallest eigenvalue, especially on graphs with large minimal valency and also on graphs with good structures. Our survey mainly consists of the following two parts: (i) Hoffman graphs, the basic theory…

Combinatorics · Mathematics 2020-11-25 Jack H. Koolen , Meng-Yue Cao , Qianqian Yang

Shearer's inequality bounds the sum of joint entropies of random variables in terms of the total joint entropy. We give another lower bound for the same sum in terms of the individual entropies when the variables are functions of…

Probability · Mathematics 2021-03-23 Endre Csóka , Viktor Harangi , Bálint Virág

This is mostly a survey paper, where we collect results concerning the spectral bounds of deterministic and random Schr\"odinger operators with complex potentials, both on \(\mathbb{R}^d\) and on compact manifolds. The survey part is…

Spectral Theory · Mathematics 2026-05-19 Eduard Stefanescu

We obtain a lower bound on each entry of the principal eigenvector of a non-regular connected graph.

Combinatorics · Mathematics 2014-03-11 Felix Goldberg

For any finite, undirected, non-bipartite, vertex-transitive graph, we establish an explicit lower bound for the smallest eigenvalue of its normalised adjacency operator, which depends on the graph only through its degree and its…

Combinatorics · Mathematics 2022-02-09 Arindam Biswas , Jyoti Prakash Saha

Let $i_t(G)$ be the number of independent sets of size $t$ in a graph $G$. Alavi, Erd\H{o}s, Malde and Schwenk made the conjecture that if $G$ is a tree then the independent set sequence $\{i_t(G)\}_{t\geq 0}$ of $G$ is unimodal; Levit and…

Combinatorics · Mathematics 2012-06-27 David Galvin

The notion of a Riordan graph was introduced recently, and it is a far-reaching generalization of the well-known Pascal graphs and Toeplitz graphs. However, apart from a certain subclass of Toeplitz graphs, nothing was known on independent…

Combinatorics · Mathematics 2020-07-01 Gi-Sang Cheon , Ji-Hwan Jung , Bumtle Kang , Hana Kim , Suh-Ryung Kim , Sergey Kitaev , Seyed Ahmad Mojallal

We prove conditions for equality between the extreme eigenvalues of a matrix and its quotient. In particular, we give a lower bound on the largest singular value of a matrix and generalize a result of Finck and Grohmann about the largest…

Combinatorics · Mathematics 2007-05-23 Bela Bollobas , Vladimir Nikiforov

Following Escobar [Esc97] and Jammes [Jam15], we introduce two types of isoperimetric constants and give lower bound estimates for the first nontrivial eigenvalues of Dirichlet-to-Neumann operators on finite graphs with boundary…

Spectral Theory · Mathematics 2017-05-15 Bobo Hua , Yan Huang , Zuoqin Wang

We prove that every 3-regular, n-vertex simple graph with sufficiently large girth contains an independent set of size at least 0.4361n. (The best known bound is 0.4352n.) In fact, computer simulation suggests that the bound our method…

Combinatorics · Mathematics 2015-12-29 Endre Csóka , Balázs Gerencsér , Viktor Harangi , Bálint Virág

We investigate the distribution of eigenvalues of weighted adjacency matrices from a specific ensemble of random graphs. We distribute $N$ vertices across a fixed number $\kappa$ of components, with asymptotically $\alpha_j \dot N$ vertices…

Mathematical Physics · Physics 2024-09-30 Valentin Vengerovsky

We study upper bounds for the first non-zero eigenvalue of the Steklov problem defined on finite graphs with boundary. For finite graphs with boundary included in a Cayley graph associated to a group of polynomial growth, we give an upper…

Spectral Theory · Mathematics 2020-11-12 Hélène Perrin

We consider the problem of bounding large deviations for non-i.i.d. random variables that are allowed to have arbitrary dependencies. Previous works typically assumed a specific dependence structure, namely the existence of independent…

Probability · Mathematics 2018-11-06 Christoph H. Lampert , Liva Ralaivola , Alexander Zimin

This paper systematically studies the behavior of the leading eigenvectors for independent edge undirected random graphs generated from a general latent position model whose link function is possibly infinite rank and also possibly…

Statistics Theory · Mathematics 2025-01-28 Minh Tang , Joshua R. Cape

We obtain eigenvalue equations satisfied by various elliptic modular graphs with five links where two of the vertices are unintegrated. Solving them leads to several non--trivial algebraic identities between these graphs.

High Energy Physics - Theory · Physics 2023-03-28 Anirban Basu