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