Book contents
- Frontmatter
- Contents
- List of Contributors
- Preface
- 1 Infinite Planar Graphs with Non-negative Combinatorial Curvature
- 2 Curvature Calculations for Antitrees
- 3 Gromov–Lawson Tunnels with Estimates
- 4 Norm Convergence of the Resolvent for Wild Perturbations
- 5 Manifolds with Ricci Curvature in the Kato Class: Heat Kernel Bounds and Applications
- 6 Multiple Boundary Representations of λ-Harmonic Functions on Trees
- 7 Internal DLA on Sierpinski Gasket Graphs
- 8 Universal Lower Bounds for Laplacians on Weighted Graphs
- 9 Critical Hardy Inequalities on Manifolds and Graphs
- 10 Neumann Domains on Graphs and Manifolds
- 11 On the Existence and Uniqueness of Self-Adjoint Realizations of Discrete (Magnetic) Schrödinger Operators
- 12 Box Spaces: Geometry of Finite Quotients
- 13 Ramanujan Graphs and Digraphs
- 14 From Partial Differential Equations to Groups
- 15 Spectral Properties of Limit-Periodic Operators
- 16 Uniform Existence of the IDS on Lattices and Groups
13 - Ramanujan Graphs and Digraphs
Published online by Cambridge University Press: 14 August 2020
- Frontmatter
- Contents
- List of Contributors
- Preface
- 1 Infinite Planar Graphs with Non-negative Combinatorial Curvature
- 2 Curvature Calculations for Antitrees
- 3 Gromov–Lawson Tunnels with Estimates
- 4 Norm Convergence of the Resolvent for Wild Perturbations
- 5 Manifolds with Ricci Curvature in the Kato Class: Heat Kernel Bounds and Applications
- 6 Multiple Boundary Representations of λ-Harmonic Functions on Trees
- 7 Internal DLA on Sierpinski Gasket Graphs
- 8 Universal Lower Bounds for Laplacians on Weighted Graphs
- 9 Critical Hardy Inequalities on Manifolds and Graphs
- 10 Neumann Domains on Graphs and Manifolds
- 11 On the Existence and Uniqueness of Self-Adjoint Realizations of Discrete (Magnetic) Schrödinger Operators
- 12 Box Spaces: Geometry of Finite Quotients
- 13 Ramanujan Graphs and Digraphs
- 14 From Partial Differential Equations to Groups
- 15 Spectral Properties of Limit-Periodic Operators
- 16 Uniform Existence of the IDS on Lattices and Groups
Summary
Ramanujan graphs have fascinating properties and history. In this paper we explore a parallel notion of Ramanujan digraphs, collecting relevant results from old and recent papers, and proving some new ones. Almost-normal Ramanujan digraphs are shown to be of special interest, as they are extreme in the sense of an Alon-Boppana theorem, and they have remarkable combinatorial features, such as small diameter, Chernoff bound for sampling, optimal covering time and sharp cutoff. Other topics explored are the connection to Cayley graphs and digraphs, the spectral radius of universal covers, Alon's conjecture for random digraphs, and explicit constructions of almost-normal Ramanujan digraphs.
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- Analysis and Geometry on Graphs and Manifolds , pp. 344 - 367Publisher: Cambridge University PressPrint publication year: 2020
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