001    package net.sf.cpsolver.studentsct.heuristics.selection;
002    
003    import java.util.Set;
004    
005    import net.sf.cpsolver.ifs.heuristics.NeighbourSelection;
006    import net.sf.cpsolver.ifs.heuristics.RoundRobinNeighbourSelection;
007    import net.sf.cpsolver.ifs.model.Neighbour;
008    import net.sf.cpsolver.ifs.solution.Solution;
009    import net.sf.cpsolver.ifs.solver.Solver;
010    import net.sf.cpsolver.ifs.util.DataProperties;
011    import net.sf.cpsolver.ifs.util.Progress;
012    import net.sf.cpsolver.ifs.util.ToolBox;
013    import net.sf.cpsolver.studentsct.model.Enrollment;
014    import net.sf.cpsolver.studentsct.model.Request;
015    import net.sf.cpsolver.studentsct.model.Student;
016    
017    /**
018     * Random unassignment of some problematic students. Problematic students are to
019     * be provided by a neighbour selection that was used before this one by
020     * {@link RoundRobinNeighbourSelection}.
021     * 
022     * <br>
023     * <br>
024     * In each step a problematic student is randomly selected with the given
025     * probabilty. Null is returned otherwise (the controll is passed to the next
026     * {@link NeighbourSelection}).
027     * 
028     * <br>
029     * <br>
030     * Parameters: <br>
031     * <table border='1'>
032     * <tr>
033     * <th>Parameter</th>
034     * <th>Type</th>
035     * <th>Comment</th>
036     * </tr>
037     * <tr>
038     * <td>Neighbour.RandomUnassignmentOfProblemStudentProb</td>
039     * <td>{@link Double}</td>
040     * <td>Probability of a random selection of a student from the given set of
041     * problematic students.</td>
042     * </tr>
043     * </table>
044     * <br>
045     * <br>
046     * 
047     * @version StudentSct 1.2 (Student Sectioning)<br>
048     *          Copyright (C) 2007 - 2010 Tomas Muller<br>
049     *          <a href="mailto:muller@unitime.org">muller@unitime.org</a><br>
050     *          <a href="http://muller.unitime.org">http://muller.unitime.org</a><br>
051     * <br>
052     *          This library is free software; you can redistribute it and/or modify
053     *          it under the terms of the GNU Lesser General Public License as
054     *          published by the Free Software Foundation; either version 3 of the
055     *          License, or (at your option) any later version. <br>
056     * <br>
057     *          This library is distributed in the hope that it will be useful, but
058     *          WITHOUT ANY WARRANTY; without even the implied warranty of
059     *          MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
060     *          Lesser General Public License for more details. <br>
061     * <br>
062     *          You should have received a copy of the GNU Lesser General Public
063     *          License along with this library; if not see
064     *          <a href='http://www.gnu.org/licenses/'>http://www.gnu.org/licenses/</a>.
065     */
066    public class RndUnProblStudSelection extends RandomUnassignmentSelection {
067        private ProblemStudentsProvider iProblemStudentsProvider = null;
068        private Set<Student> iProblemStudents = null;
069    
070        /**
071         * Constructor
072         * 
073         * @param properties
074         *            configuration
075         * @param psp
076         *            a class that provides the set of problematic students
077         */
078        public RndUnProblStudSelection(DataProperties properties, ProblemStudentsProvider psp) {
079            super(properties);
080            iProblemStudentsProvider = psp;
081            iRandom = properties.getPropertyDouble("Neighbour.RandomUnassignmentOfProblemStudentProb", 0.9);
082        }
083    
084        /**
085         * Initialization -- {@link ProblemStudentsProvider#getProblemStudents()} is
086         * called
087         */
088        @Override
089        public void init(Solver<Request, Enrollment> solver) {
090            iProblemStudents = iProblemStudentsProvider.getProblemStudents();
091            Progress.getInstance(solver.currentSolution().getModel()).setPhase(
092                    "Random unassignment of problematic students...", 1);
093        }
094    
095        /**
096         * With the given probabilty, a problematic student is randomly selected to
097         * be unassigned. Null is returned otherwise.
098         */
099        @Override
100        public Neighbour<Request, Enrollment> selectNeighbour(Solution<Request, Enrollment> solution) {
101            if (!iProblemStudents.isEmpty() && Math.random() < iRandom) {
102                Student student = ToolBox.random(iProblemStudents);
103                iProblemStudents.remove(student);
104                return new UnassignStudentNeighbour(student);
105            }
106            Progress.getInstance(solution.getModel()).incProgress();
107            return null;
108        }
109    }