Random sampling and approximation of MAX-CSPs

  • Authors:
  • Noga Alon;W. Fernandez de la Vega;Ravi Kannan;Marek Karpinski

  • Affiliations:
  • Department of Mathematics, Tel Aviv University, 69978 Tel Aviv, Israel;CNRS, Universite Paris Sud, Orsay, Paris, France;Department of Computer Science, Yale University, New Haven, CT;Department of Computer Science, University of Bonn, Germany

  • Venue:
  • Journal of Computer and System Sciences - STOC 2002
  • Year:
  • 2003

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Abstract

In a maximum-r-constraint satisfaction problem with variables {x1, x2, ... ,xn}, we are given Boolean functions f1, f2, ..., fm each involving r of the n variables and are to find the maximum number of these functions that can be made true by a truth assignment to the variables. We show that for r fixed, there is an integer q ∈ O(log(1/ε)/ε4) such that if we choose q variables (uniformly) at random, the answer to the subproblem induced on the chosen variables is, with high probability, within an additive error of εqr of qr/nr times the answer to the original n-variable problem. The previous best result for the case of r = 2 (which includes many graph problems) was that there is an algorithm which given the induced sub-problem on q = O(1/ε5) variables, can find an approximation to the answer to the whole problem within additive error εn2. For r≥3, the conference version of this paper (in: Proceedings of the 34th ACM STOC, ACM, New York, 2002, pp. 232-239) and independently Andersson and Engebretsen give the first results with sample complexity q dependent only polynomially upon 1/ε. Their algorithm has a sample complexity q of O(1/ε7). They (as also the earlier papers) however do not directly prove any relation between the answer to the sub-problem and the whole problem as we do here. Our method also differs from other results in that it is linear algebraic, rather than combinatorial in nature.