ramanujan-expander

Construct and verify Ramanujan graphs for spectral edge expansion under degree constraints.

60|13|Updated Dec 22, 2025
One-click install
npx skills add https://github.com/plurigrid/asi --skill ramanujan-expander
Or copy as Structured Prompt for Agent
Please help me install this Agent Skill.
Skill: ramanujan-expander
Source: https://github.com/plurigrid/asi/tree/main/skills/ramanujan-expander
Command: npx skills add https://github.com/plurigrid/asi --skill ramanujan-expander

SYSTEM DOCUMENTATION & REQUIREMENTS

What problem does it solve?

Ramanujan graphs are optimal spectral expanders; this skill covers their theory, edge-growth rules, and spectral centrality.

Core Features & Use Cases

  • Alon-Boppana verification: check spectral bounds
  • Edge-growth rules: preserve Ramanujan property during growth
  • Centrality & mixing: spectral methods for network analysis

Quick Start

Check a given d-regular graph for λ₂ ≤ 2√(d-1) and use LPS construction to build Ramanujan graphs.

Frequently Asked Questions about ramanujan-expander

High-intent search queries and answers about installing and using this skill.

FAQPage Schema
How do I verify that a d-regular graph is a Ramanujan expander?

A d-regular graph is a Ramanujan expander if its second-largest eigenvalue λ₂ satisfies λ₂ ≤ 2√(d-1), the Alon-Boppana bound. Use eigenvalue computation to check this spectral condition and confirm optimal edge expansion properties.

What is the LPS construction and how does it build Ramanujan graphs?

LPS construction is an explicit method for building d-regular Ramanujan graphs using algebraic number theory. It generates optimal spectral expanders that achieve the theoretical lower bound on the second eigenvalue for degree-constrained networks.

How do I maintain Ramanujan properties when growing a d-regular network incrementally?

Apply edge-growth rules that preserve the spectral bound λ₂ ≤ 2√(d-1) during expansion. Use non-backtracking methods and spectral verification at each growth step to ensure the graph remains a Ramanujan expander.

When should I use spectral expanders for network topology optimization?

Use spectral expanders when you need networks with minimal mixing time and maximal edge connectivity under degree constraints. Ramanujan graphs optimize these properties, making them ideal for distributed systems, peer-to-peer networks, and fault-tolerant topology design.

Can I use non-backtracking eigenvalue methods to audit spectral properties?

Yes. Non-backtracking methods provide rigorous spectral property auditing by computing eigenvalues that detect community structure and verify expansion bounds. This complements traditional eigenvalue analysis for comprehensive network centrality checks.

What are the limitations of Ramanujan graph construction at large scales?

LPS construction requires algebraic number-theoretic setup that scales with degree. Computational complexity and memory grow with network size; verification of the Alon-Boppana bound becomes expensive for very large graphs. Trade-offs exist between explicit construction and approximation methods.