Probabilistic Analysis of Optimization Problems on Generalized Random Shortest Path Metrics

TL;DR

This paper extends probabilistic analysis of optimization heuristics from Euclidean to generalized random shortest path metrics on Erdős-Rényi graphs, showing constant expected approximation ratios and polynomial bounds on heuristic iterations.

Contribution

It generalizes previous results to non-complete graphs, especially Erdős-Rényi graphs, and analyzes the performance of several heuristics on these probabilistic metric instances.

Findings

Greedy heuristic for maximum matching has a constant expected approximation ratio.

Nearest neighbor and insertion heuristics for TSP achieve constant expected approximation ratios.

2-opt heuristic for TSP has a polynomial upper bound on expected iterations.

Abstract

Simple heuristics often show a remarkable performance in practice for optimization problems. Worst-case analysis often falls short of explaining this performance. Because of this, "beyond worst-case analysis" of algorithms has recently gained a lot of attention, including probabilistic analysis of algorithms. The instances of many optimization problems are essentially a discrete metric space. Probabilistic analysis for such metric optimization problems has nevertheless mostly been conducted on instances drawn from Euclidean space, which provides a structure that is usually heavily exploited in the analysis. However, most instances from practice are not Euclidean. Little work has been done on metric instances drawn from other, more realistic, distributions. Some initial results have been obtained by Bringmann et al. (Algorithmica, 2013), who have used random shortest path metrics on complete graphs to analyze heuristics. The goal of this paper is to generalize these findings to non-complete graphs, especially Erd\H{o}s-R\'enyi random graphs. A random shortest path metric is constructed by drawing independent random edge weights for each edge in the graph and setting the distance between every pair of vertices to the length of a shortest path between them with respect to the drawn weights. For such instances, we prove that the greedy heuristic for the minimum distance maximum matching problem, the nearest neighbor and insertion heuristics for the traveling salesman problem, and a trivial heuristic for the $k$-median problem all achieve a constant expected approximation ratio. Additionally, we show a polynomial upper bound for the expected number of iterations of the 2-opt heuristic for the traveling salesman problem.