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Merge pull request #45 from hdbeukel/tabuvariant
first-best-admissible tabu search
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src/main/java/org/jamesframework/core/search/algo/tabu/FirstBestAdmissibleTabuSearch.java
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| package org.jamesframework.core.search.algo.tabu; | ||
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| import java.util.List; | ||
| import java.util.Collections; | ||
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| import org.jamesframework.core.exceptions.IncompatibleTabuMemoryException; | ||
| import org.jamesframework.core.exceptions.JamesRuntimeException; | ||
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| import org.jamesframework.core.problems.Problem; | ||
| import org.jamesframework.core.problems.sol.Solution; | ||
| import org.jamesframework.core.search.neigh.Move; | ||
| import org.jamesframework.core.search.neigh.Neighbourhood; | ||
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| /** | ||
| * <p> | ||
| * Tabu search algorithm using first-best-admissible move strategy. | ||
| * In every search step, the possible moves are evaluated in random order (shuffled). | ||
| * The first encountered admissible improvement is accepted, i.e. the first valid non-tabu | ||
| * move that yields a positive delta, if any. Else, the best admissible move, in this case | ||
| * the one with the least negative delta, is performed, as in ordinary tabu search | ||
| * (see {@link org.jamesframework.core.search.algo.tabu.TabuSearch}). | ||
| * </p> | ||
| * <p> | ||
| * This tabu search implementation includes an aspiration criterion that always accepts all moves | ||
| * that yield an improvement over the currently known best solution, even if they have been declared tabu. | ||
| * </p> | ||
| * <p> | ||
| * The search terminates in case all valid neighbours of the current solution are tabu and do not improve the | ||
| * best known solution. Note that this may never happen, which means that a stop criterion should preferably | ||
| * be specified to ensure termination. | ||
| * </p> | ||
| * | ||
| * @param <SolutionType> solution type of the problems that may be solved using this search, | ||
| * required to extend {@link Solution} | ||
| * @author <a href="mailto:chenhuanfa@gmail.com">Huanfa Chen</a>, | ||
| * <a href="mailto:herman.debeukelaer@ugent.be">Herman De Beukelaer</a> | ||
| */ | ||
| public class FirstBestAdmissibleTabuSearch<SolutionType extends Solution> extends TabuSearch<SolutionType> { | ||
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| /** | ||
| * Creates a new tabu search, specifying the problem to solve, the neighbourhood used to modify the current | ||
| * solution and the applied tabu memory. None of the arguments can be <code>null</code>. The search name defaults | ||
| * to "FirstBestAdmissibleTabuSearch". | ||
| * <p> | ||
| * Note that the applied neighbourhood and tabu memory should be compatible in terms of generated and accepted move | ||
| * types, respectively, else an {@link IncompatibleTabuMemoryException} might be thrown during search. | ||
| * | ||
| * @param problem problem to solve | ||
| * @param neighbourhood neighbourhood used to create neighbouring solutions | ||
| * @param tabuMemory applied tabu memory | ||
| * @throws NullPointerException if <code>problem</code>, <code>neighbourhood</code> or <code>tabuMemory</code> | ||
| * are <code>null</code> | ||
| */ | ||
| public FirstBestAdmissibleTabuSearch(Problem<SolutionType> problem, | ||
| Neighbourhood<? super SolutionType> neighbourhood, | ||
| TabuMemory<SolutionType> tabuMemory) { | ||
| this(null, problem, neighbourhood, tabuMemory); | ||
| } | ||
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| /** | ||
| * Creates a new tabu search, specifying the problem to solve, the neighbourhood used to modify the current | ||
| * solution, the applied tabu memory and a custom search name. The problem, neighbourhood and tabu memory can | ||
| * not be <code>null</code>. The search name can be <code>null</code> in which case the default name | ||
| * "FirstBestAdmissibleTabuSearch" is assigned. | ||
| * <p> | ||
| * Note that the applied neighbourhood and tabu memory should be compatible in terms of generated and accepted move | ||
| * types, respectively, else an {@link IncompatibleTabuMemoryException} might be thrown during search. | ||
| * | ||
| * @param name custom search name | ||
| * @param problem problem to solve | ||
| * @param neighbourhood neighbourhood used to create neighbouring solutions | ||
| * @param tabuMemory applied tabu memory | ||
| * @throws NullPointerException if <code>problem</code>, <code>neighbourhood</code> or <code>tabyMemory</code> | ||
| * are <code>null</code> | ||
| */ | ||
| public FirstBestAdmissibleTabuSearch(String name, Problem<SolutionType> problem, | ||
| Neighbourhood<? super SolutionType> neighbourhood, | ||
| TabuMemory<SolutionType> tabuMemory){ | ||
| super(name != null ? name : "FirstBestAdmissibleTabuSearch", problem, neighbourhood, tabuMemory); | ||
| } | ||
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| /** | ||
| * One step of the first-best-admissible tabu search algorithm. | ||
| * All possible moves are inspected in random order, and either the first admissible improvement, | ||
| * if any, or, else, the best admissible move, is applied to the current solution. | ||
| * | ||
| * @throws IncompatibleTabuMemoryException if the applied tabu memory is not compatible with the type of moves | ||
| * generated by the applied neighbourhood | ||
| * @throws JamesRuntimeException if depending on malfunctioning components (problem, neighbourhood, ...) | ||
| */ | ||
| @Override | ||
| protected void searchStep() { | ||
| // get list of possible moves | ||
| List<? extends Move<? super SolutionType>> moves = getNeighbourhood().getAllMoves(getCurrentSolution()); | ||
| // shuffle moves | ||
| Collections.shuffle(moves); | ||
| // find best admissible move, or first admissible improvement (if any) | ||
| Move<? super SolutionType> move = getBestMove( | ||
| // inspect all moves | ||
| moves, | ||
| // not necessarily an improvement | ||
| false, | ||
| // return first improvement move, if any | ||
| true, | ||
| // filter tabu moves (with aspiration criterion) | ||
| getTabuFilter() | ||
| ); | ||
| // process chosen move | ||
| if (move != null) { | ||
| // accept move (automatically updates tabu memory) | ||
| accept(move); | ||
| } else { | ||
| // no valid non-tabu neighbour found: terminate search | ||
| stop(); | ||
| } | ||
| } | ||
| } |
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