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28
Planning as satisfiability
 IN ECAI92
, 1992
"... We develop a formal model of planning based on satisfiability rather than deduction. The satis ability approach not only provides a more flexible framework for stating di erent kinds of constraints on plans, but also more accurately reflects the theory behind modern constraintbased planning systems ..."
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Cited by 501 (27 self)
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We develop a formal model of planning based on satisfiability rather than deduction. The satis ability approach not only provides a more flexible framework for stating di erent kinds of constraints on plans, but also more accurately reflects the theory behind modern constraintbased planning systems. Finally, we consider the computational characteristics of the resulting formulas, by solving them with two very different satisfiability testing procedures.
Incorporation of Temporal Logic Control into Plan Operators
 In ECAI
, 2000
"... . Domainspecific control information is often essential in solving difficult planning problems efficiently. Temporal logics are a declarative and expressive representation for such control information. In this paper we investigate the integration of temporal logic control information into plan oper ..."
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Cited by 23 (0 self)
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. Domainspecific control information is often essential in solving difficult planning problems efficiently. Temporal logics are a declarative and expressive representation for such control information. In this paper we investigate the integration of temporal logic control information into plan operators. For a given control formula \Phi and operators O, we produce a new set O \Phi of operators that works like O under the control of \Phi. We show that for a subclass of temporal logic formulae the compilation causes only a lowpolynomial increase in the size of the operators, that the length of plans is not affected, and that the speedup obtained is competitive with what is achieved with temporal logic control as formula progression. The translation uses operators with conditional effects. An important benefit of our approach is that the problem of using temporal logic formulae as control information is solved once and for all: temporal logic control can be implemented as a preprocessi...
Symmetry Reduction for SAT Representations of Transition Systems
"... Symmetries are inherent in systems that consist of several interchangeable objects or components. When reasoning about such systems, big computational savings can be obtained if the presence of symmetries is recognized. In earlier work, symmetries in constraint satisfaction problems have been h ..."
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Cited by 19 (2 self)
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Symmetries are inherent in systems that consist of several interchangeable objects or components. When reasoning about such systems, big computational savings can be obtained if the presence of symmetries is recognized. In earlier work, symmetries in constraint satisfaction problems have been handled by introducing symmetrybreaking constraints.
Balanced Incomplete Block Design as Satisfiability
 In Proceedings of the 12th Irish Conference on Artificial Intelligence and Cognitive Science
, 2001
"... Balanced incomplete block design generation is a standard combinatorial problem from design theory. Constraint programming has recently been applied to the problem using a mixture of binary and nonbinary constraints, with special techniques for symmetry breaking. We describe a new binary constraint ..."
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Cited by 18 (3 self)
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Balanced incomplete block design generation is a standard combinatorial problem from design theory. Constraint programming has recently been applied to the problem using a mixture of binary and nonbinary constraints, with special techniques for symmetry breaking. We describe a new binary constraint model and apply search algorithms indirectly via satis ability encoding. The encoded problems turn out to be hard for current algorithms, and symmetry breaking sometimes makes them harder, but the results suggest a promising direct approach.
Lifted Search Engines for Satisfiability
, 1999
"... There are several powerful solvers for satisfiability (SAT), such as wsat, DavisPutnam, and relsat. However, in practice, the SAT encodings often have so many clauses that we exceed physical memory resources on attempting to solve them. This excessive size often arises because conversion to SAT, ..."
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Cited by 18 (4 self)
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There are several powerful solvers for satisfiability (SAT), such as wsat, DavisPutnam, and relsat. However, in practice, the SAT encodings often have so many clauses that we exceed physical memory resources on attempting to solve them. This excessive size often arises because conversion to SAT, from a more natural encoding using quantifications over domains, requires expanding quantifiers. This suggests that we should "lift" successful SAT solvers. That is, adapt the solvers to use quantified clauses instead of ground clauses. However, it was generally believed that such lifted solvers would be impractical: Partially, because of the overhead of handling the predicates and quantifiers, and partially because lifting would not allow essential indexing and caching schemes. Here we show that, to the contrary, it is not only practical to handle quantified clauses directly, but that lifting can give exponential savings. We do this by identifying certain tasks that are central to...
FirstSolution Search with Symmetry Breaking and Implied Constraints
 Proceedings of the CP'01 Workshop on Modelling and Problem Formulation
"... Symmetry breaking and implied constraints can speed up both exhaustive search and the search for a single solution. We experiment with both types of constraint, using three search algorithms (backtracking, local and hybrid) to find single solutions for SAT encodings of three combinatorial problems ( ..."
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Cited by 11 (5 self)
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Symmetry breaking and implied constraints can speed up both exhaustive search and the search for a single solution. We experiment with both types of constraint, using three search algorithms (backtracking, local and hybrid) to find single solutions for SAT encodings of three combinatorial problems (clique, set cover and balanced incomplete block design generation). Both show strong positive and negative effects, depending on the problem class and algorithm. However, symmetry breaking constraints consistently have a negative effect on the incomplete search algorithms. This suggests an opposite strategy when applying stochastic search: maximising symmetry in the constraint model.
Multiple sequence alignment
 Protein Structure Prediction — Methods and Protocols
, 2000
"... Multiple sequence alignment is a central problem in Bioinformatics and a challenging one for optimisation algorithms. An established integer programming approach is to apply branchandcut to a graphtheoretical model. The models are exponentially large but are represented intensionally, and violate ..."
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Cited by 9 (1 self)
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Multiple sequence alignment is a central problem in Bioinformatics and a challenging one for optimisation algorithms. An established integer programming approach is to apply branchandcut to a graphtheoretical model. The models are exponentially large but are represented intensionally, and violated constraints can be located in polynomial time. This report describes a new integer program formulation that generates polynomialsized models small enough to be passed to generic solvers. It is a hybrid formulation relating the sparse alignment graph with a compact encoding of the alignment matrix via channelling constraints. Alignments obtained with a pseudoBoolean local search algorithm are competitive with those of stateoftheart algorithms. Execution times are much longer, but in future work we aim to develop a more efficient specialised algorithm. 1
Actionspace partitioning for planning
 In Proceedings of the National Conference on Artificial Intelligence
, 2007
"... For autonomous artificial decisionmakers to solve realistic tasks, they need to deal with searching through large state and action spaces under time pressure. We study the problem of planning in such domains and show how structured representations of the environment’s dynamics can help partition th ..."
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Cited by 8 (0 self)
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For autonomous artificial decisionmakers to solve realistic tasks, they need to deal with searching through large state and action spaces under time pressure. We study the problem of planning in such domains and show how structured representations of the environment’s dynamics can help partition the action space into a set of equivalence classes at run time. The partitioned action space is then used to produce a reduced set of actions. This technique speeds up search and can yield significant gains in planning efficiency.
The Complexity of SymmetryBreaking Formulas
 Annals of Mathematics and Artificial Intelligence
, 2002
"... Symmetrybreaking formulas for a constraintsatisfaction problem are satisifed by exactly one member (e.g., the lexicographic leader) from each set of \symmetrical points" in the search space. Thus, the incorporation of such formulas can accelerate the search for a solution without sacrificing ..."
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Cited by 8 (1 self)
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Symmetrybreaking formulas for a constraintsatisfaction problem are satisifed by exactly one member (e.g., the lexicographic leader) from each set of \symmetrical points" in the search space. Thus, the incorporation of such formulas can accelerate the search for a solution without sacrificing satisfiability.
Plan permutation symmetries as a source of planner inefficiency
 In Proc. of UK Workshop on Planning and Scheduling
, 2003
"... This paper briefly reviews sources of symmetry in planning and highlights one source that has not previously been tackled: plan permutation symmetry. Symmetries can be a significant problem for efficiency of planning systems, as has been previously observed in the treatment of other forms of symmetr ..."
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Cited by 4 (1 self)
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This paper briefly reviews sources of symmetry in planning and highlights one source that has not previously been tackled: plan permutation symmetry. Symmetries can be a significant problem for efficiency of planning systems, as has been previously observed in the treatment of other forms of symmetry in planning problems. We examine how plan permutation symmetries can be eliminated and present evidence to support the claim that these symmetries are an important problem for planning systems.