    001package org.cpsolver.studentsct.heuristics;
    002
    003import java.util.Collections;
    004import java.util.Comparator;
    005import java.util.HashMap;
    006import java.util.Iterator;
    007import java.util.List;
    008import java.util.Set;
    009
    010import org.cpsolver.ifs.assignment.Assignment;
    011import org.cpsolver.ifs.heuristics.BacktrackNeighbourSelection;
    012import org.cpsolver.ifs.util.DataProperties;
    013import org.cpsolver.studentsct.StudentSectioningModel;
    014import org.cpsolver.studentsct.model.CourseRequest;
    015import org.cpsolver.studentsct.model.Enrollment;
    016import org.cpsolver.studentsct.model.Request;
    017
    018
    019/**
    020 * Randomized backtracking-based neighbour selection. This class extends
    021 * {@link RandomizedBacktrackNeighbourSelection}, however, only a randomly
    022 * selected subset of enrollments of each request is considered (
    023 * {@link CourseRequest#computeRandomEnrollments(Assignment, int)} with the given limit is
    024 * used).
    025 *
    026 * <br>
    027 * <br>
    028 * Parameters: <br>
    029 * <table border='1'><caption>Related Solver Parameters</caption>
    030 * <tr>
    031 * <th>Parameter</th>
    032 * <th>Type</th>
    033 * <th>Comment</th>
    034 * </tr>
    035 * <tr>
    036 * <td>Neighbour.MaxValues</td>
    037 * <td>{@link Integer}</td>
    038 * <td>Limit on the number of enrollments to be visited of each
    039 * {@link CourseRequest}.</td>
    040 * </tr>
    041 * </table>
    042 * <br>
    043 * <br>
    044 *
    045 * @author  Tomáš Müller
    046 * @version StudentSct 1.3 (Student Sectioning)<br>
    047 *          Copyright (C) 2007 - 2014 Tomáš Müller<br>
    048 *          <a href="mailto:muller@unitime.org">muller@unitime.org</a><br>
    049 *          <a href="http://muller.unitime.org">http://muller.unitime.org</a><br>
    050 * <br>
    051 *          This library is free software; you can redistribute it and/or modify
    052 *          it under the terms of the GNU Lesser General Public License as
    053 *          published by the Free Software Foundation; either version 3 of the
    054 *          License, or (at your option) any later version. <br>
    055 * <br>
    056 *          This library is distributed in the hope that it will be useful, but
    057 *          WITHOUT ANY WARRANTY; without even the implied warranty of
    058 *          MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
    059 *          Lesser General Public License for more details. <br>
    060 * <br>
    061 *          You should have received a copy of the GNU Lesser General Public
    062 *          License along with this library; if not see
    063 *          <a href='http://www.gnu.org/licenses/'>http://www.gnu.org/licenses/</a>.
    064 */
    065public class RandomizedBacktrackNeighbourSelection extends BacktrackNeighbourSelection<Request, Enrollment> {
    066    private int iMaxValues = 100;
    067    private boolean iPreferPriorityStudents = true;
    068
    069    /**
    070     * Constructor
    071     *
    072     * @param properties
    073     *            configuration
    074     * @throws Exception thrown when the initialization fails
    075     */
    076    public RandomizedBacktrackNeighbourSelection(DataProperties properties) throws Exception {
    077        super(properties);
    078        iMaxValues = properties.getPropertyInt("Neighbour.MaxValues", iMaxValues);
    079        iPreferPriorityStudents = properties.getPropertyBoolean("Sectioning.PriorityStudentsFirstSelection.AllIn", true);
    080    }
    081
    082    /**
    083     * List of values of a variable.
    084     * {@link CourseRequest#computeRandomEnrollments(Assignment, int)} with the provided
    085     * limit is used for a {@link CourseRequest}.
    086     */
    087    @Override
    088    protected Iterator<Enrollment> values(BacktrackNeighbourSelection<Request, Enrollment>.BacktrackNeighbourSelectionContext context, Request variable) {
    089        if (variable instanceof CourseRequest) {
    090            final CourseRequest request = (CourseRequest)variable;
    091            final StudentSectioningModel model = (StudentSectioningModel)context.getModel();
    092            final Assignment<Request, Enrollment> assignment = context.getAssignment();
    093            final Enrollment current = assignment.getValue(request);
    094            List<Enrollment> values = (iMaxValues > 0 ? request.computeRandomEnrollments(assignment, iMaxValues) : request.computeEnrollments(assignment));
    095            Collections.sort(values, new Comparator<Enrollment>() {
    096                private HashMap<Enrollment, Double> iValues = new HashMap<Enrollment, Double>();
    097                private Double value(Enrollment e) {
    098                    Double value = iValues.get(e);
    099                    if (value == null) {
    100                        if (model.getStudentQuality() != null)
    101                            value = model.getStudentWeights().getWeight(assignment, e, model.getStudentQuality().conflicts(e));
    102                        else
    103                            value = model.getStudentWeights().getWeight(assignment, e,
    104                                    (model.getDistanceConflict() == null ? null : model.getDistanceConflict().conflicts(e)),
    105                                    (model.getTimeOverlaps() == null ? null : model.getTimeOverlaps().conflicts(e)));
    106                        iValues.put(e, value);
    107                    }
    108                    return value;
    109                }
    110                @Override
    111                public int compare(Enrollment e1, Enrollment e2) {
    112                    if (e1.equals(e2)) return 0;
    113                    if (e1.equals(current)) return -1;
    114                    if (e2.equals(current)) return 1;
    115                    Double v1 = value(e1), v2 = value(e2);
    116                    return v1.equals(v2) ? e1.compareTo(assignment, e2) : v2.compareTo(v1);
    117                }
    118            });
    119            return values.iterator();
    120        } else {
    121            return variable.computeEnrollments(context.getAssignment()).iterator();
    122        }
    123    }
    124
    125    /**
    126     * Check if the given conflicting enrollment can be unassigned
    127     * @param conflict given enrollment
    128     * @return if running MPP, do not unassign initial enrollments
    129     */
    130    public boolean canUnassign(Enrollment enrollment, Enrollment conflict, Assignment<Request, Enrollment> assignment) {
    131        if (conflict.getRequest().isMPP() && conflict.equals(conflict.getRequest().getInitialAssignment()) &&
    132                !enrollment.equals(enrollment.getRequest().getInitialAssignment())) return false;
    133        if (conflict.getRequest() instanceof CourseRequest && ((CourseRequest)conflict.getRequest()).getFixedValue() != null) return false;
    134        if (conflict.getRequest().getStudent().hasMinCredit()) {
    135            float credit = conflict.getRequest().getStudent().getAssignedCredit(assignment) - conflict.getCredit();
    136            if (credit < conflict.getRequest().getStudent().getMinCredit()) return false;
    137        }
    138        if (!conflict.getRequest().isAlternative() && conflict.getRequest().getRequestPriority().isHigher(enrollment.getRequest())) return false;
    139        if (iPreferPriorityStudents || conflict.getRequest().getRequestPriority().isSame(enrollment.getRequest())) {
    140            if (conflict.getStudent().getPriority().isHigher(enrollment.getStudent())) return false;
    141        }
    142        return true;
    143    }
    144
    145    @Override
    146    protected boolean checkBound(List<Request> variables2resolve, int idx, int depth, Enrollment value, Set<Enrollment> conflicts) {
    147        for (Enrollment conflict: conflicts)
    148            if (!canUnassign(value, conflict, getContext().getAssignment())) return false;
    149        return super.checkBound(variables2resolve, idx, depth, value, conflicts);
    150    }
    151}