Probabilistically Estimating Backbones and Variable Bias: Experimental Overview

  • Authors:
  • Eric I. Hsu;Christian J. Muise;J. Christopher Beck;Sheila A. Mcilraith

  • Affiliations:
  • Department of Computer Science, University of Toronto,;Department of Computer Science, University of Toronto,;Department of Computer Science, University of Toronto,;Department of Computer Science, University of Toronto,

  • Venue:
  • CP '08 Proceedings of the 14th international conference on Principles and Practice of Constraint Programming
  • Year:
  • 2008

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Abstract

Backbone variables have the same assignment in all solutions to a given constraint satisfaction problem; more generally, biasrepresents the proportion of solutions that assign a variable a particular value. Intuitively such constructs would seem important to efficient search, but their study to date has been from a mostly conceptual perspective, in terms of indicating problem hardness or motivating and interpreting heuristics. Here we summarize a two-phase project where we first measure the ability of both existing and novel probabilistic message-passing techniques to directly estimate bias and identify backbones for the Boolean Satisfiability (SAT) Problem. We confirm that methods like Belief Propagation and Survey Propagation---plus Expectation Maximization-based variants---do produce good estimates with distinctive properties. The second phase demonstrates the use of bias estimation within a modern SAT solver, exhibiting a correlation between accurate, stable, estimates and successful backtracking search. The same process also yields a family of search heuristics that can dramatically improve search efficiency for the hard random problems considered.