Discrete quantitative nodal theorem

Abstract

We prove a theorem that can be thought of as a common generalization of the Discrete Nodal Theorem and (one direction of) Cheeger's Inequality for graphs. special case of this result will assert that if the second and third eigenvalues of the Laplacian are at least c apart, then the subgraphs induced by the positive and negative supports of the eigenvector belonging to the second eigenvalue are not only connected, but edge-expanders (in a weighted sense, with expansion depending on c).