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- Steven David Prestwich
- SAT
- 2005

Many current local search algorithms for SAT fall into one of two classes. Random walk algorithms such as Walksat/SKC, Novelty+ and HWSAT are very successful but can be trapped for long periods in deep local minima. Clause weighting algorithms such as DLM, GLS, ESG and SAPS are good at escaping local minima but require expensive smoothing phases in whichâ€¦ (More)

- Steven David Prestwich
- Discrete Applied Mathematics
- 2008

The IMPASSE class of local search algorithms have given good results on many vertex colouring benchmarks. Previous work enhanced IMPASSE by adding the constraint programming technique of forward checking, in order to prune colouration neighbourhoods during search. On several large graphs the algorithm found the best known colourings. This paper extends theâ€¦ (More)

A combination of local search and constraint propagation called FCNS has previously been described for pure graph colouring. FCNS is a hybrid of the DSATUR backtracker and the IMPASSE local search algorithm, restricting coloration neighbourhoods by propagation, and dynamically ordering vertices by the BrÃ©laz heuristic. We extend it to bandwidth colouringâ€¦ (More)

- Steven David Prestwich
- CP
- 2000

This paper addresses the following question: what is the essential difference between stochastic local search (LS) and systematic backtracking (BT) that gives LS superior scalability? One possibility is LSâ€™s lack of firm commitment to any variable assignment. Three BT algorithms are modified to have this feature by introducing randomness into the choice ofâ€¦ (More)

- Steven David Prestwich
- Annals of Mathematics and Artificial Intelligence
- 2002

Two contrasting search paradigms for solving combinatorial problems are systematic backtracking and local search. The former is often effective on highly structured problems because of its ability to exploit consistency techniques, while the latter tends to scale better on very large problems. Neither approach is ideal for all problems, and a current trendâ€¦ (More)

- Carmel Domshlak, Steven David Prestwich, Francesca De Rossi, Kristen Brent Venable, Toby Walsh
- J. Heuristics
- 2006

Many real life optimization problems are defined in terms of both hard and soft constraints, and qualitative conditional preferences. However, there is as yet no single framework for combined reasoning about these three kinds of information. In this paper we study how to exploit classical and soft constraint solvers for handling qualitative preferenceâ€¦ (More)

- Steven David Prestwich
- Discrete Applied Mathematics
- 2003

- Brahim Hnich, Steven David Prestwich, Evgeny Selensky, Barbara M. Smith
- Constraints
- 2006

Covering arrays can be applied to the testing of software, hardware and advanced materials, and to the effects of hormone interaction on gene expression. In this paper we develop constraint programming models of the problem of finding an optimal covering array. Our models exploit global constraints, multiple viewpoints and symmetry-breaking constraints. Weâ€¦ (More)

- Steven David Prestwich
- PEPM
- 1993

Partial deduction systems must be guided by an unfolding strategy, telling them which atoms to unfold and when to stop unfolding. Online strategies exploit knowledge accumulated during the unfolding itself, for example in a goal stack, while offline strategies are fixed before unfolding begins. Online strategies are more powerful, but a major overhead forâ€¦ (More)