001package org.cpsolver.studentsct.heuristics.selection;
002
003import java.util.Set;
004
005import org.cpsolver.ifs.heuristics.NeighbourSelection;
006import org.cpsolver.ifs.heuristics.RoundRobinNeighbourSelection;
007import org.cpsolver.ifs.model.Neighbour;
008import org.cpsolver.ifs.solution.Solution;
009import org.cpsolver.ifs.solver.Solver;
010import org.cpsolver.ifs.util.DataProperties;
011import org.cpsolver.ifs.util.Progress;
012import org.cpsolver.ifs.util.ToolBox;
013import org.cpsolver.studentsct.model.Enrollment;
014import org.cpsolver.studentsct.model.Request;
015import org.cpsolver.studentsct.model.Request.RequestPriority;
016import org.cpsolver.studentsct.model.Student;
017
018
019/**
020 * Random unassignment of some problematic students. Problematic students are to
021 * be provided by a neighbour selection that was used before this one by
022 * {@link RoundRobinNeighbourSelection}.
023 * 
024 * <br>
025 * <br>
026 * In each step a problematic student is randomly selected with the given
027 * probabilty. Null is returned otherwise (the controll is passed to the next
028 * {@link NeighbourSelection}).
029 * 
030 * <br>
031 * <br>
032 * Parameters: <br>
033 * <table border='1'><caption>Related Solver Parameters</caption>
034 * <tr>
035 * <th>Parameter</th>
036 * <th>Type</th>
037 * <th>Comment</th>
038 * </tr>
039 * <tr>
040 * <td>Neighbour.RandomUnassignmentOfProblemStudentProb</td>
041 * <td>{@link Double}</td>
042 * <td>Probability of a random selection of a student from the given set of
043 * problematic students.</td>
044 * </tr>
045 * </table>
046 * <br>
047 * <br>
048 * 
049 * @author  Tomáš Müller
050 * @version StudentSct 1.3 (Student Sectioning)<br>
051 *          Copyright (C) 2007 - 2014 Tomáš Müller<br>
052 *          <a href="mailto:muller@unitime.org">muller@unitime.org</a><br>
053 *          <a href="http://muller.unitime.org">http://muller.unitime.org</a><br>
054 * <br>
055 *          This library is free software; you can redistribute it and/or modify
056 *          it under the terms of the GNU Lesser General Public License as
057 *          published by the Free Software Foundation; either version 3 of the
058 *          License, or (at your option) any later version. <br>
059 * <br>
060 *          This library is distributed in the hope that it will be useful, but
061 *          WITHOUT ANY WARRANTY; without even the implied warranty of
062 *          MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
063 *          Lesser General Public License for more details. <br>
064 * <br>
065 *          You should have received a copy of the GNU Lesser General Public
066 *          License along with this library; if not see
067 *          <a href='http://www.gnu.org/licenses/'>http://www.gnu.org/licenses/</a>.
068 */
069public class RndUnProblStudSelection extends RandomUnassignmentSelection {
070    private ProblemStudentsProvider iProblemStudentsProvider = null;
071    private Set<Student> iProblemStudents = null;
072
073    /**
074     * Constructor
075     * 
076     * @param properties
077     *            configuration
078     * @param psp
079     *            a class that provides the set of problematic students
080     */
081    public RndUnProblStudSelection(DataProperties properties, ProblemStudentsProvider psp) {
082        super(properties);
083        iProblemStudentsProvider = psp;
084        iRandom = properties.getPropertyDouble("Neighbour.RandomUnassignmentOfProblemStudentProb", 0.9);
085    }
086
087    /**
088     * Initialization -- {@link ProblemStudentsProvider#getProblemStudents()} is
089     * called
090     */
091    @Override
092    public void init(Solver<Request, Enrollment> solver) {
093        iProblemStudents = iProblemStudentsProvider.getProblemStudents();
094        Progress.getInstance(solver.currentSolution().getModel()).setPhase(
095                "Random unassignment of problematic students...", 1);
096    }
097
098    /**
099     * With the given probabilty, a problematic student is randomly selected to
100     * be unassigned. Null is returned otherwise.
101     */
102    @Override
103    public synchronized Neighbour<Request, Enrollment> selectNeighbour(Solution<Request, Enrollment> solution) {
104        if (Math.random() < iRandom) {
105            while (!iProblemStudents.isEmpty()) {
106                Student student = ToolBox.random(iProblemStudents);
107                iProblemStudents.remove(student);
108                if (student.hasMinCredit() && student.getAssignedCredit(solution.getAssignment()) < student.getMinCredit()) continue;
109                return new UnassignStudentNeighbour(student, solution.getAssignment(), RequestPriority.Important);
110            }
111        }
112        Progress.getInstance(solution.getModel()).incProgress();
113        return null;
114    }
115}