Random independent sets and local sparsity

Abstract

We analyze random constructions of independent sets in locally sparse graphs, specifically graphs with bounded maximum average degree in neighborhoods or with fractionally $r$-colorable neighborhoods. Specializing our methods to finding large independent sets and low-weight fractional colorings, we focus on optimizing for marginals, but we also derive results that find many independent sets (i.e.\ give lower bounds on the independence polynomial) by optimizing for entropy. Our main results generalize the local Shearer bound of Martinsson and Steiner for triangle-free graphs to graphs with few triangles and to graphs with fractionally $r$-colorable neighborhoods, in the latter case improving upon a result of Dhawan. We also extend independence polynomial bounds obtained via induction to such graphs, improving upon known bounds obtained by local occupancy by relaxing the necessary hypotheses from a maximum degree condition to an average degree condition.