Strongly regular graph

Summary

A strongly regular graph is a regular graph with a second kind of regularity. The number of common neighbours of two distinct vertices depends only on whether they are adjacent. Its parameters are written $(v, k, \lambda, \mu)$. A connected strongly regular graph that is not complete has exactly three distinct adjacency eigenvalues. These graphs are a meeting point of graph theory, design theory and group theory. The node strongly regular graph gives the precise definition.