# Improved Distributed Approximations for Maximum Independent Set

## TL;DR

This paper introduces a randomized distributed algorithm that efficiently approximates the maximum-weight independent set problem within a small factor, significantly improving speed over previous methods in the CONGEST model.

## Contribution

It provides the first exponential speed-up for approximating MaxIS with a small approximation loss in distributed models.

## Key findings

- Achieves a $(1+ ext{epsilon}) imes ext{Delta}$-approximation in poly(log log n)/epsilon rounds.
- Runs exponentially faster than previous algorithms for similar approximation guarantees.
- Shows that approximating MaxIS is exponentially easier than finding a maximal independent set.

## Abstract

We present improved results for approximating maximum-weight independent set ($\MaxIS$) in the CONGEST and LOCAL models of distributed computing. Given an input graph, let $n$ and $\Delta$ be the number of nodes and maximum degree, respectively, and let $\MIS(n,\Delta)$ be the the running time of finding a \emph{maximal} independent set ($\MIS$) in the CONGEST model. Bar-Yehuda et al. [PODC 2017] showed that there is an algorithm in the CONGEST model that finds a $\Delta$-approximation for $\MaxIS$ in $O(\MIS(n,\Delta)\log W)$ rounds, where $W$ is the maximum weight of a node in the graph, which can be as high as $\poly (n)$. Whether their algorithm is deterministic or randomized depends on the $\MIS$ algorithm that is used as a black-box. Our main result in this work is a randomized $(\poly(\log\log n)/\epsilon)$-round algorithm that finds, with high probability, a $(1+\epsilon)\Delta$-approximation for $\MaxIS$ in the CONGEST model. That is, by sacrificing only a tiny fraction of the approximation guarantee, we achieve an \emph{exponential} speed-up in the running time over the previous best known result. Due to a lower bound of $\Omega(\sqrt{\log n/\log \log n})$ that was given by Kuhn, Moscibroda and Wattenhofer [JACM, 2016] on the number of rounds for any (possibly randomized) algorithm that finds a maximal independent set (even in the LOCAL model) this result implies that finding a $(1+\epsilon)\Delta$-approximation for $\MaxIS$ is exponentially easier than $\MIS$.