Random 2-SAT: results and problems

  • Authors:
  • W. Fernandez de la Vega

  • Affiliations:
  • Univ. de Paris-Sud, Orsay, France

  • Venue:
  • Theoretical Computer Science - Phase transitions in combinatorial problems
  • Year:
  • 2001

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Abstract

In the random 2-SAT problem, we are given a set C of m disjunctions of two literals chosen at random within the ( 2n2 ) pairs of distinct literals coming from n logical variables. The basic problem is to /nd out for which values of the ratio _=m=n the disjunctions in C are almost surely simultaneously satisfiable (or almost surely not simultaneously satisfiable) as n tends to infinity. The purpose of this paper is to review the main steps in the solution of this problem, starting with the location of the asymptotic critical ratio around 8 years ago and ending with the recent almost complete solution due to Bollob4as et al. Thus, this paper is not a review in the usual sense of the word, i.e., it does not include all the known results about random 2-SAT. We will also make a few comments concerning the behaviour of the number of satisfying assignments of random instances of 2-SAT below the critical ratio, a problem relevant to theoretical physics.