001package net.sf.cpsolver.studentsct.heuristics.selection;
002
003import net.sf.cpsolver.ifs.heuristics.NeighbourSelection;
004import net.sf.cpsolver.ifs.heuristics.ValueSelection;
005import net.sf.cpsolver.ifs.heuristics.VariableSelection;
006import net.sf.cpsolver.ifs.model.Neighbour;
007import net.sf.cpsolver.ifs.model.SimpleNeighbour;
008import net.sf.cpsolver.ifs.solution.Solution;
009import net.sf.cpsolver.ifs.solver.Solver;
010import net.sf.cpsolver.ifs.util.DataProperties;
011import net.sf.cpsolver.ifs.util.Progress;
012import net.sf.cpsolver.studentsct.model.Enrollment;
013import net.sf.cpsolver.studentsct.model.Request;
014
015/**
016 * Use the provided variable and value selection for some time. The provided
017 * variable and value selection is used for the number of iterations equal to
018 * the number of all variables in the problem. If a complete solution is found,
019 * the neighbour selection is stopped (it returns null).
020 * 
021 * <br>
022 * <br>
023 * Parameters: <br>
024 * <table border='1'>
025 * <tr>
026 * <th>Parameter</th>
027 * <th>Type</th>
028 * <th>Comment</th>
029 * </tr>
030 * <tr>
031 * <td>Neighbour.StandardIterations</td>
032 * <td>{@link Long}</td>
033 * <td>Number of iterations to perform. If -1, number of iterations is set to
034 * the number of unassigned variables.</td>
035 * </tr>
036 * </table>
037 * <br>
038 * <br>
039 * 
040 * @version StudentSct 1.2 (Student Sectioning)<br>
041 *          Copyright (C) 2007 - 2010 Tomáš Müller<br>
042 *          <a href="mailto:muller@unitime.org">muller@unitime.org</a><br>
043 *          <a href="http://muller.unitime.org">http://muller.unitime.org</a><br>
044 * <br>
045 *          This library is free software; you can redistribute it and/or modify
046 *          it under the terms of the GNU Lesser General Public License as
047 *          published by the Free Software Foundation; either version 3 of the
048 *          License, or (at your option) any later version. <br>
049 * <br>
050 *          This library is distributed in the hope that it will be useful, but
051 *          WITHOUT ANY WARRANTY; without even the implied warranty of
052 *          MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
053 *          Lesser General Public License for more details. <br>
054 * <br>
055 *          You should have received a copy of the GNU Lesser General Public
056 *          License along with this library; if not see
057 *          <a href='http://www.gnu.org/licenses/'>http://www.gnu.org/licenses/</a>.
058 */
059public class StandardSelection implements NeighbourSelection<Request, Enrollment> {
060    private long iIteration = 0;
061    private ValueSelection<Request, Enrollment> iValueSelection = null;
062    private VariableSelection<Request, Enrollment> iVariableSelection = null;
063    protected long iNrIterations = -1;
064
065    /**
066     * Constructor (variable and value selection are expected to be already
067     * initialized).
068     * 
069     * @param properties
070     *            configuration
071     * @param variableSelection
072     *            variable selection
073     * @param valueSelection
074     *            value selection
075     */
076    public StandardSelection(DataProperties properties, VariableSelection<Request, Enrollment> variableSelection,
077            ValueSelection<Request, Enrollment> valueSelection) {
078        iVariableSelection = variableSelection;
079        iValueSelection = valueSelection;
080    }
081
082    /** Initialization */
083    @Override
084    public void init(Solver<Request, Enrollment> solver) {
085        iIteration = solver.currentSolution().getIteration();
086        iNrIterations = solver.getProperties().getPropertyLong("Neighbour.StandardIterations", -1);
087        if (iNrIterations > 0)
088            Progress.getInstance(solver.currentSolution().getModel()).setPhase("Ifs...", iNrIterations);
089    }
090
091    /**
092     * Employ the provided {@link VariableSelection} and {@link ValueSelection}
093     * and return the selected value as {@link SimpleNeighbour}. The selection
094     * is stopped (null is returned) after the number of iterations equal to the
095     * number of variables in the problem or when a complete solution is found.
096     */
097    @Override
098    public Neighbour<Request, Enrollment> selectNeighbour(Solution<Request, Enrollment> solution) {
099        if (iNrIterations < 0) {
100            iNrIterations = solution.getModel().unassignedVariables().size();
101            Progress.getInstance(solution.getModel()).setPhase("Ifs...", iNrIterations);
102        }
103        if (solution.getModel().unassignedVariables().isEmpty()
104                || solution.getIteration() >= iIteration + iNrIterations)
105            return null;
106        Progress.getInstance(solution.getModel()).incProgress();
107        for (int i = 0; i < 10; i++) {
108            Request request = iVariableSelection.selectVariable(solution);
109            Enrollment enrollment = (request == null ? null : (Enrollment) iValueSelection.selectValue(solution,
110                    request));
111            if (enrollment != null && !enrollment.variable().getModel().conflictValues(enrollment).contains(enrollment))
112                return new SimpleNeighbour<Request, Enrollment>(request, enrollment);
113        }
114        return null;
115    }
116
117}