Tag - Graph theory
A d-regular graph is Ramanujan if its non-trivial eigenvalues in absolute value are bounded by 2√(d-1). Recently Adam Marcus, Daniel Spielman and Nikhil Srivastava gave a positive answer to this question by showing that any bipartite d-regular Ramanujan graph has a 2-fold cover that is also Ramanujan. In this talk we shall discuss their approach and mention similarities with function field towers.
A two-hour course on expanders, thin subgroups of Lie groups, and superstrong approximation.
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