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}