A Polynomial Regularity Lemma for Semialgebraic Hypergraphs and Its Applications in Geometry and Property Testing

Fox, Gromov, Lafforgue, Naor, and Pach proved a regularity lemma for semi-algebraic kuniform hypergraphs of bounded complexity, showing that for each ǫ > 0 the vertex set can be equitably partitioned into a bounded number of parts (in terms of ǫ and the complexity) so that all but an ǫ-fraction of the k-tuples of parts are homogeneous. We prove that the number of parts can be taken to be polynomial in 1/ǫ. Our improved regularity lemma can be applied to geometric problems and to the following general question on property testing: is it possible to decide, with query complexity polynomial in the reciprocal of the approximation parameter, whether a hypergraph has a given hereditary property? We give an affirmative answer for testing typical hereditary properties for semi-algebraic hypergraphs of bounded complexity.