001package org.cpsolver.studentsct.heuristics.selection;
002
003import java.util.HashMap;
004import java.util.List;
005import java.util.Map;
006
007import org.cpsolver.ifs.assignment.Assignment;
008import org.cpsolver.ifs.heuristics.NeighbourSelection;
009import org.cpsolver.ifs.model.Neighbour;
010import org.cpsolver.ifs.solution.Solution;
011import org.cpsolver.ifs.solver.Solver;
012import org.cpsolver.ifs.util.DataProperties;
013import org.cpsolver.ifs.util.Progress;
014import org.cpsolver.ifs.util.ToolBox;
015import org.cpsolver.studentsct.StudentSectioningModel;
016import org.cpsolver.studentsct.model.Enrollment;
017import org.cpsolver.studentsct.model.Request;
018import org.cpsolver.studentsct.model.Student;
019
020
021/**
022 * Random unassignment of some (randomly selected) students.
023 * 
024 * <br>
025 * <br>
026 * In each step a student is randomly selected with the given probabilty. Null
027 * is returned otherwise (controll is passed to the following
028 * {@link NeighbourSelection}).
029 * 
030 * <br>
031 * <br>
032 * Parameters: <br>
033 * <table border='1' summary='Related Solver Parameters'>
034 * <tr>
035 * <th>Parameter</th>
036 * <th>Type</th>
037 * <th>Comment</th>
038 * </tr>
039 * <tr>
040 * <td>Neighbour.RandomUnassignmentProb</td>
041 * <td>{@link Double}</td>
042 * <td>Probability of a random selection of a student.</td>
043 * </tr>
044 * </table>
045 * <br>
046 * <br>
047 * 
048 * @version StudentSct 1.3 (Student Sectioning)<br>
049 *          Copyright (C) 2007 - 2014 Tomas Muller<br>
050 *          <a href="mailto:muller@unitime.org">muller@unitime.org</a><br>
051 *          <a href="http://muller.unitime.org">http://muller.unitime.org</a><br>
052 * <br>
053 *          This library is free software; you can redistribute it and/or modify
054 *          it under the terms of the GNU Lesser General Public License as
055 *          published by the Free Software Foundation; either version 3 of the
056 *          License, or (at your option) any later version. <br>
057 * <br>
058 *          This library is distributed in the hope that it will be useful, but
059 *          WITHOUT ANY WARRANTY; without even the implied warranty of
060 *          MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
061 *          Lesser General Public License for more details. <br>
062 * <br>
063 *          You should have received a copy of the GNU Lesser General Public
064 *          License along with this library; if not see
065 *          <a href='http://www.gnu.org/licenses/'>http://www.gnu.org/licenses/</a>.
066 */
067public class RandomUnassignmentSelection implements NeighbourSelection<Request, Enrollment> {
068    private List<Student> iStudents = null;
069    protected double iRandom = 0.5;
070
071    /**
072     * Constructor
073     * 
074     * @param properties
075     *            configuration
076     */
077    public RandomUnassignmentSelection(DataProperties properties) {
078        iRandom = properties.getPropertyDouble("Neighbour.RandomUnassignmentProb", iRandom);
079    }
080
081    /**
082     * Initialization
083     */
084    @Override
085    public void init(Solver<Request, Enrollment> solver) {
086        iStudents = ((StudentSectioningModel) solver.currentSolution().getModel()).getStudents();
087        Progress.getInstance(solver.currentSolution().getModel()).setPhase("Random unassignment...", 1);
088    }
089
090    /**
091     * With the given probabilty, a student is randomly selected to be
092     * unassigned. Null is returned otherwise.
093     */
094    @Override
095    public Neighbour<Request, Enrollment> selectNeighbour(Solution<Request, Enrollment> solution) {
096        if (Math.random() < iRandom) {
097            Student student = ToolBox.random(iStudents);
098            return new UnassignStudentNeighbour(student);
099        }
100        Progress.getInstance(solution.getModel()).incProgress();
101        return null;
102    }
103
104    /** Unassignment of all requests of a student */
105    public static class UnassignStudentNeighbour implements Neighbour<Request, Enrollment> {
106        private Student iStudent = null;
107
108        /**
109         * Constructor
110         * 
111         * @param student
112         *            a student to be unassigned
113         */
114        public UnassignStudentNeighbour(Student student) {
115            iStudent = student;
116        }
117
118        @Override
119        public double value(Assignment<Request, Enrollment> assignment) {
120            double val = 0;
121            for (Request request : iStudent.getRequests()) {
122                Enrollment enrollment = assignment.getValue(request);
123                if (enrollment != null)
124                    val -= enrollment.toDouble(assignment);
125            }
126            return val;
127        }
128
129        /** All requests of the given student are unassigned */
130        @Override
131        public void assign(Assignment<Request, Enrollment> assignment, long iteration) {
132            for (Request request : iStudent.getRequests())
133                assignment.unassign(iteration, request);
134        }
135
136        @Override
137        public String toString() {
138            StringBuffer sb = new StringBuffer("Un{");
139            sb.append(" " + iStudent);
140            sb.append(" }");
141            return sb.toString();
142        }
143
144        @Override
145        public Map<Request, Enrollment> assignments() {
146            Map<Request, Enrollment> ret = new HashMap<Request, Enrollment>();
147            for (Request request : iStudent.getRequests())
148                ret.put(request, null);
149            return ret;
150        }
151
152    }
153
154}