Abstract.A simple yet successful approach to parallel satisfiability (SAT) solving is to run several different (a portfolio of) SAT solvers on the input problem at the same time until one solver finds a solution. The SAT solvers in the portfolio can be instances of a single solver with different configuration settings. Additionally the solvers can exchange information usually in the form of clauses. In this paper we investigate whether this approach is applicable in the case of massively parallel SAT solving. Our solver is intended to run on clusters with thousands of processors, hence the name HordeSat. HordeSat is a fully distributed portfolio-based SAT solver with a modular design that allows it to use any SAT solver that implements a given interface. HordeSat has a decentralized design and features hierarchical parallelism with interleaved communication and search. We experimentally evaluated it using all the benchmark problems from the application tracks of the 2011 and 2014 International SAT Competitions. The experiments demonstrate that HordeSat is scalable up to hundreds or even thousands of processors achieving significant speedups especially for hard instances.

No abstract

No abstract

Abstract. Blocked clause elimination is a powerful technique in SAT solving. In recent work, it has been shown that it is possible to decompose any propositional formula into two subsets (blocked sets) such that both can be solved by blocked clause elimination. We extend this work in several ways. First, we prove new theoretical properties of blocked sets. We then present additional and improved ways to efficiently solve blocked sets. Further, we propose novel decomposition algorithms for faster decomposition or which produce blocked sets with desirable attributes. We use decompositions to reencode CNF formulas and to obtain circuits, such as AIGs, which can then be simplified by algorithms from circuit synthesis and encoded back to CNF. Our experiments demonstrate that these techniques can increase the performance of the SAT solver Lingeling on hard to solve application benchmarks.

We give an overview of SAT Competition 2016, the 2016 edition of thefamous competition for Boolean satisfiability (SAT) solvers with over 20 years of history. A key aim is to point out ``what's hot'' in SAT competitions in 2016, i.e., new developments in thecompetition series, including new competition tracks and new solver techniquesimplemented in some of the award-winning solvers.