Size Versus Stability in the Marriage Problem

  • Authors:
  • Péter Biró;David F. Manlove;Shubham Mittal

  • Affiliations:
  • Department of Computing Science, University of Glasgow, Glasgow, UK G12 8QQ;Department of Computing Science, University of Glasgow, Glasgow, UK G12 8QQ;Department of Computer Science and Engineering, Block VI, Indian Institute of Technology, Delhi, Hauz Khas, New Delhi, India 110 016

  • Venue:
  • Approximation and Online Algorithms
  • Year:
  • 2009

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Abstract

Given an instance I of the classical Stable Marriage problem with Incomplete preference lists (smi), a maximum cardinality matching can be larger than a stable matching. In many large-scale applications of smi, we seek to match as many agents as possible. This motivates the problem of finding a maximum cardinality matching in I that admits the smallest number of blocking pairs (so is “as stable as possible”). We show that this problem is NP-hard and not approximable within n 1 − ε , for any ε 0, unless P=NP, where n is the number of men in I. Further, even if all preference lists are of length at most 3, we show that the problem remains NP-hard and not approximable within Δ, for some Δ 1. By contrast, we give a polynomial-time algorithm for the case where the preference lists of one sex are of length at most 2.