In Proceedings of the 12th NASA formal methods symposium (NFM’20)
Abstract In the context of parallel SATisfiability solving, this paper presents an implementation and evaluation of a clause strengthening algorithm. The developed component can be easily combined with (virtually) any CDCL-like SAT solver. Our implementation is integrated as a part of Painless, a generic and modular framework for building parallel SAT solvers.
In Proceedings of the 23rd international conference on theory and applications of satisfiability testing (SAT’20)
Abstract Modern parallel SAT solvers rely heavily on effective clause sharing policies for their performance. The core problem being addressed by these policies can be succinctly stated as “the problem of identifying high-quality learnt clauses” that when shared between the worker nodes of parallel solvers results in improved performance than otherwise. The term “high-quality clauses” is often defined in terms of metrics that solver designers have identified over years of empirical study.
In Proceedings of the 25th international conference on tools and algorithms for the construction and analysis of systems (TACAS’19)
Abstract Over the last decade, parallel SATisfiability solving has been widely studied from both theoretical and practical aspects. There are two main approaches. First, divide-and-conquer (D&C) splits the search space, each solver being in charge of a particular subspace. The second one, portfolio launches multiple solvers in parallel, and the first to find a solution ends the computation. However although D&C based approaches seem to be the natural way to work in parallel, portfolio ones experimentally provide better performances.
In Proceedings of the 24th international conference on tools and algorithms for the construction and analysis of systems (TACAS’18)
Abstract SAT solvers are now widely used to solve a large variety of problems, including formal verification of systems. SAT problems derived from such applications often exhibit symmetry properties that could be exploited to speed up their solving. Static symmetry breaking is so far the most popular approach to take advantage of symmetries. It relies on a symmetry preprocessor which augments the initial problem with constraints that force the solver to consider only a few configurations among the many symmetric ones.
In Proceedings of the 20th international conference on theory and applications of satisfiability testing (SAT’17)
Abstract Over the last decade, parallel SAT solving has been widely studied from both theoretical and practical aspects. There are now numerous solvers that dier by parallelization strategies, programming languages, concurrent programming, involved libraries, etc. Hence, comparing the eciency of the theoretical approaches is a challenging task. Moreover, the introduction of a new approach needs either a deep understanding of the existing solvers, or to start from scratch the implementation of a new tool.
In Proceedings of the 14th international symposium on automated technology for verification and analysis (ATVA’16)
Abstract Checking liveness properties with partial-order reductions requires a cycle proviso to ensure that an action cannot be postponed forever. The proviso forces each cycle to contain at least one fully expanded state. We present new heuristics to select which state to expand, hoping to reduce the size of the resulting graph. The choice of the state to expand is done when encountering a dangerous edge. Almost all existing provisos expand the source of this edge, while this paper also explores the expansion of the destination and the use of SCC-based information.
In International Journal on Software Tools for Technology Transfer (STTT)
Abstract We present new parallel explicit emptiness checks for LTL model checking. Unlike existing parallel emptiness checks, these are based on a Strongly Connected Component (SCC) enumeration, support generalized Büchi acceptance, and require no synchronization points nor recomputing procedures. A salient feature of our algorithms is the use of a global union-find data structure in which multiple threads share structural information about the automaton checked. Besides these basic algorithms, we present one architectural variant isolating threads that write to the union-find, and one extension that decomposes the automaton based on the strength of its SCCs to use more optimized emptiness checks.
In Proceedings of the 19th international conference on tools and algorithms for the construction and analysis of systems (TACAS’15)
Abstract We present new parallel emptiness checks for LTL model checking. Unlike existing parallel emptiness checks, these are based on an SCC enumeration, support generalized Buchi acceptance, and require no synchronization points nor repair procedures. A salient feature of our algorithms is the use of a global union-find data structure in which multiple threads share structural information about the automaton being checked. Our prototype implementation has encouraging performances: the new emptiness checks have better speedup than existing algorithms in half of our experiments.
In Proceedings of the 20th international conference on tools and algorithms for the construction and analysis of systems (TACAS’14)
Abstract In a previous work, we showed that a kind of $\omega$-automata known as Transition-based Generalized Testing Automata (TGTA) can outperform the Büchi automata traditionally used for explicit model checking when verifying stutter-invariant properties. In this work, we investigate the use of these generalized testing automata to improve symbolic model checking of stutter-invariant LTL properties. We propose an efficient symbolic encoding of stuttering transitions in the product between a model and a TGTA.
In Proceedings of the 19th international conference on logic for programming, artificial intelligence, and reasoning (LPAR’13)
Abstract The automata-theoretic approach for the verification of linear time properties involves checking the emptiness of a Büchi automaton. However generalized Büchi automata, with multiple acceptance sets, are preferred when verifying under weak fairness hypotheses. Existing emptiness checks for which the complexity is independent of the number of acceptance sets are all based on the enumeration of Strongly Connected Components (SCCs). In this paper, we review the state of the art SCC enumeration algorithms to study how they can be turned into emptiness checks.
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