001package org.cpsolver.studentsct.heuristics;
002
003import org.cpsolver.ifs.heuristics.RouletteWheelSelection;
004import org.cpsolver.ifs.heuristics.VariableSelection;
005import org.cpsolver.ifs.solution.Solution;
006import org.cpsolver.ifs.solver.Solver;
007import org.cpsolver.ifs.util.DataProperties;
008import org.cpsolver.studentsct.StudentSectioningModel;
009import org.cpsolver.studentsct.model.Enrollment;
010import org.cpsolver.studentsct.model.Request;
011
012/**
013 * Variable ({@link Request}) selection using {@link RouletteWheelSelection}.
014 * Unassigned request has 10 points, an assigned request has 1 point for each
015 * section that exceeds its bound.
016 * 
017 * <br>
018 * <br>
019 * 
020 * @version StudentSct 1.3 (Student Sectioning)<br>
021 *          Copyright (C) 2007 - 2014 Tomáš Müller<br>
022 *          <a href="mailto:muller@unitime.org">muller@unitime.org</a><br>
023 *          <a href="http://muller.unitime.org">http://muller.unitime.org</a><br>
024 * <br>
025 *          This library is free software; you can redistribute it and/or modify
026 *          it under the terms of the GNU Lesser General Public License as
027 *          published by the Free Software Foundation; either version 3 of the
028 *          License, or (at your option) any later version. <br>
029 * <br>
030 *          This library is distributed in the hope that it will be useful, but
031 *          WITHOUT ANY WARRANTY; without even the implied warranty of
032 *          MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
033 *          Lesser General Public License for more details. <br>
034 * <br>
035 *          You should have received a copy of the GNU Lesser General Public
036 *          License along with this library; if not see
037 *          <a href='http://www.gnu.org/licenses/'>http://www.gnu.org/licenses/</a>.
038 */
039public class RouletteWheelRequestSelection implements VariableSelection<Request, Enrollment> {
040    RouletteWheelSelection<Request> iRoulette = null;
041
042    /**
043     * Constructor
044     * 
045     * @param properties
046     *            configuration
047     */
048    public RouletteWheelRequestSelection(DataProperties properties) {
049        super();
050    }
051
052    /** Initialization */
053    @Override
054    public void init(Solver<Request, Enrollment> solver) {
055
056    }
057
058    /** Populate roulette wheel selection, if null or empty. 
059     * @param solution current solution
060     * @return selection
061     **/
062    protected RouletteWheelSelection<Request> getRoulette(Solution<Request, Enrollment> solution) {
063        if (iRoulette != null && iRoulette.hasMoreElements()) {
064            if (iRoulette.getUsedPoints() < 0.1 * iRoulette.getTotalPoints())
065                return iRoulette;
066        }
067        iRoulette = new RouletteWheelSelection<Request>();
068        for (Request request : ((StudentSectioningModel) solution.getModel()).variables()) {
069            double points = 0;
070            if (solution.getAssignment().getValue(request) == null)
071                points += 10;
072            else {
073                Enrollment enrollment = solution.getAssignment().getValue(request);
074                if (enrollment.toDouble(solution.getAssignment()) > request.getBound())
075                    points += 1;
076            }
077            if (points > 0)
078                iRoulette.add(request, points);
079        }
080        return iRoulette;
081    }
082
083    /**
084     * Variable selection. {@link RouletteWheelSelection} is used. Unassigned
085     * request has 10 points, an assigned request has 1 point for each section
086     * that exceeds its bound.
087     */
088    @Override
089    public synchronized Request selectVariable(Solution<Request, Enrollment> solution) {
090        return getRoulette(solution).nextElement();
091    }
092}