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Subject: lazy clause generation × Subject: constraint programming × Subject: boolean satisfiability × Author: Downing, Nicholas Ronald ×

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    Scheduling and rostering with learning constraint solvers
    Downing, Nicholas Ronald ( 2016)
    In this research we investigate using Constraint Programming (CP) with Lazy Clause Generation (LCG), that is, constraint solvers with nogood learning, to tackle a number of well known scheduling, rostering, and planning problems. We extend a number of CP constraints to be useable in an LCG solver, and we investigate alternative search strategies that use the Unsatisfiable Cores, i.e. reasons for failure returned by the LCG solver, to guide the search for optimal solutions. We give comprehensive analysis and experiments. These experiments show that while adding more and more sophisticated constraint propagators to LCG delivers diminishing returns, unsatisfiable-core optimization which leverages the infrastructure provided by LCG can deliver significant benefits which are unavailable in CP without LCG. Overall, we demonstrate that LCG is a highly competitive technology for solving realistic industrial scheduling and rostering problems to optimality, allowing that the problems are smaller than those tackled by competing algorithms which do not prove optimality.