Please help transcribe this video using our simple transcription tool. You need to be logged in to do so.

Description

Given a set system (V,S), V=[n] and S={S_1,ldots,S_m}, the minimum discrepancy problem is to find a 2-coloring X:V -> {-1,+1}, such that each set is colored as evenly as possible, i.e. find X to minimize max_{j in [m]} |sum_{i in S_j} X(i)|. In this paper we give the first polynomial time algorithms for discrepancy minimization, that achieve bounds similar to those known existentially using the so-called Entropy Method. We also give a first approximation-like result for discrepancy. Specifically we give efficient randomized algorithms to: 1. Construct an $O(sqrt{n})$ discrepancy coloring for general sets systems when $m=O(n)$, matching the celebrated result of Spencer up to constant factors. Previously, no algorithmic guarantee better than the random coloring bound, i.e. O((n log n)^{1/2}), was known. More generally, for $mgeq n$, we obtain a discrepancy bound of O(n^{1/2} log (2m/n)). 2. Construct a coloring with discrepancy $O(t^{1/2} log n)$, if each element lies in at most $t$ sets. This matches the (non-constructive) result of Srinivasan cite{Sr}. 3. Construct a coloring with discrepancy O(lambdalog(nm)), where lambda is the hereditary discrepancy of the set system. In particular, this implies a logarithmic approximation for hereditary discrepancy. The main idea in our algorithms is to gradually produce a coloring by solving a sequence of semidefinite programs, while using the entropy method to guide the choice of the semidefinite program at each stage.

Questions and Answers

You need to be logged in to be able to post here.