001package org.cpsolver.studentsct.constraint;
002
003import java.util.ArrayList;
004import java.util.List;
005import java.util.Set;
006
007import org.cpsolver.ifs.assignment.Assignment;
008import org.cpsolver.ifs.model.GlobalConstraint;
009import org.cpsolver.ifs.util.DataProperties;
010import org.cpsolver.ifs.util.ToolBox;
011import org.cpsolver.studentsct.StudentSectioningModel;
012import org.cpsolver.studentsct.model.Course;
013import org.cpsolver.studentsct.model.Enrollment;
014import org.cpsolver.studentsct.model.Request;
015
016
017/**
018 * Course limit constraint. This global constraint ensures that a limit of each
019 * course is not exceeded. This means that the total sum of weights of course
020 * requests (see {@link Request#getWeight()}) enrolled into a course is below
021 * the course's limit (see {@link Course#getLimit()}).
022 * 
023 * <br>
024 * <br>
025 * Sections with negative limit are considered unlimited, and therefore
026 * completely ignored by this constraint.
027 * 
028 * <br>
029 * <br>
030 * Parameters:
031 * <table border='1' summary='Related Solver Parameters'>
032 * <tr>
033 * <th>Parameter</th>
034 * <th>Type</th>
035 * <th>Comment</th>
036 * </tr>
037 * <tr>
038 * <td>CourseLimit.PreferDummyStudents</td>
039 * <td>{@link Boolean}</td>
040 * <td>If true, requests of dummy (last-like) students are preferred to be
041 * selected as conflicting.</td>
042 * </tr>
043 * </table>
044 * <br>
045 * <br>
046 * 
047 * @version StudentSct 1.3 (Student Sectioning)<br>
048 *          Copyright (C) 2007 - 2014 Tomas Muller<br>
049 *          <a href="mailto:muller@unitime.org">muller@unitime.org</a><br>
050 *          <a href="http://muller.unitime.org">http://muller.unitime.org</a><br>
051 * <br>
052 *          This library is free software; you can redistribute it and/or modify
053 *          it under the terms of the GNU Lesser General Public License as
054 *          published by the Free Software Foundation; either version 3 of the
055 *          License, or (at your option) any later version. <br>
056 * <br>
057 *          This library is distributed in the hope that it will be useful, but
058 *          WITHOUT ANY WARRANTY; without even the implied warranty of
059 *          MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
060 *          Lesser General Public License for more details. <br>
061 * <br>
062 *          You should have received a copy of the GNU Lesser General Public
063 *          License along with this library; if not see
064 *          <a href='http://www.gnu.org/licenses/'>http://www.gnu.org/licenses/</a>.
065 */
066public class CourseLimit extends GlobalConstraint<Request, Enrollment> {
067    private static double sNominalWeight = 0.00001;
068    private boolean iPreferDummyStudents = false;
069
070    /**
071     * Constructor
072     * 
073     * @param cfg
074     *            solver configuration
075     */
076    public CourseLimit(DataProperties cfg) {
077        super();
078        iPreferDummyStudents = cfg.getPropertyBoolean("CourseLimit.PreferDummyStudents", false);
079    }
080
081
082    /**
083     * Enrollment weight of a course if the given request is assigned. In order
084     * to overcome rounding problems with last-like students ( e.g., 5 students
085     * are projected to two sections of limit 2 -- each section can have up to 3
086     * of these last-like students), the weight of the request with the highest
087     * weight in the section is changed to a small nominal weight.
088     * 
089     * @param assignment current assignment
090     * @param course
091     *            a course that is of concern
092     * @param request
093     *            a request of a student to be assigned containing the given
094     *            section
095     * @return section's new weight
096     */
097    public static double getEnrollmentWeight(Assignment<Request, Enrollment> assignment, Course course, Request request) {
098        return course.getEnrollmentWeight(assignment, request) + request.getWeight() - Math.max(course.getMaxEnrollmentWeight(assignment), request.getWeight()) + sNominalWeight;
099    }
100
101    /**
102     * A given enrollment is conflicting, if the course's enrollment
103     * (computed by {@link CourseLimit#getEnrollmentWeight(Assignment, Course, Request)})
104     * exceeds the limit. <br>
105     * If the limit is breached, one or more existing enrollments are
106     * (randomly) selected as conflicting until the overall weight is under the
107     * limit.
108     * 
109     * @param enrollment
110     *            {@link Enrollment} that is being considered
111     * @param conflicts
112     *            all computed conflicting requests are added into this set
113     */
114    @Override
115    public void computeConflicts(Assignment<Request, Enrollment> assignment, Enrollment enrollment, Set<Enrollment> conflicts) {
116        // check reservation can assign over the limit
117        if (((StudentSectioningModel)getModel()).getReservationCanAssignOverTheLimit() &&
118            enrollment.getReservation() != null && enrollment.getReservation().canAssignOverLimit())
119            return;
120
121        // enrollment's course
122        Course course = enrollment.getCourse();
123
124        // exclude free time requests
125        if (course == null)
126            return;
127
128        // unlimited course
129        if (course.getLimit() < 0)
130            return;
131        
132        // new enrollment weight
133        double enrlWeight = getEnrollmentWeight(assignment, course, enrollment.getRequest());
134
135        // below limit -> ok
136        if (enrlWeight <= course.getLimit())
137            return;
138
139        // above limit -> compute adepts (current assignments that are not
140        // yet conflicting)
141        // exclude all conflicts as well
142        List<Enrollment> adepts = new ArrayList<Enrollment>(course.getEnrollments(assignment).size());
143        for (Enrollment e : course.getEnrollments(assignment)) {
144            if (e.getRequest().equals(enrollment.getRequest()))
145                continue;
146            if (conflicts.contains(e))
147                enrlWeight -= e.getRequest().getWeight();
148            else
149                adepts.add(e);
150        }
151
152        // while above limit -> pick an adept and make it conflicting
153        while (enrlWeight > course.getLimit()) {
154            if (adepts.isEmpty()) {
155                // no adepts -> enrollment cannot be assigned
156                conflicts.add(enrollment);
157                break;
158            }
159            
160            // pick adept (prefer dummy students), decrease unreserved space,
161            // make conflict
162            List<Enrollment> best = new ArrayList<Enrollment>();
163            boolean bestDummy = false;
164            double bestValue = 0;
165            for (Enrollment adept: adepts) {
166                boolean dummy = adept.getStudent().isDummy();
167                double value = adept.toDouble(assignment, false);
168                
169                if (iPreferDummyStudents && dummy != bestDummy) {
170                    if (dummy) {
171                        best.clear();
172                        best.add(adept);
173                        bestDummy = dummy;
174                        bestValue = value;
175                    }
176                    continue;
177                }
178                
179                if (best.isEmpty() || value > bestValue) {
180                    if (best.isEmpty()) best.clear();
181                    best.add(adept);
182                    bestDummy = dummy;
183                    bestValue = value;
184                } else if (bestValue == value) {
185                    best.add(adept);
186                }
187            }
188            
189            Enrollment conflict = ToolBox.random(best);
190            adepts.remove(conflict);
191            enrlWeight -= conflict.getRequest().getWeight();
192            conflicts.add(conflict);
193        }
194    }
195
196    /**
197     * A given enrollment is conflicting, if the course's enrollment (computed by
198     * {@link CourseLimit#getEnrollmentWeight(Assignment, Course, Request)}) exceeds the
199     * limit.
200     * 
201     * @param enrollment
202     *            {@link Enrollment} that is being considered
203     * @return true, if the enrollment cannot be assigned without exceeding the limit
204     */
205    @Override
206    public boolean inConflict(Assignment<Request, Enrollment> assignment, Enrollment enrollment) {
207        // check reservation can assign over the limit
208        if (((StudentSectioningModel)getModel()).getReservationCanAssignOverTheLimit() &&
209            enrollment.getReservation() != null && enrollment.getReservation().canAssignOverLimit())
210            return false;
211
212        // enrollment's course
213        Course course = enrollment.getCourse();
214
215        // exclude free time requests
216        if (course == null)
217            return false;
218
219        // unlimited course
220        if (course.getLimit() < 0)
221            return false;
222
223
224        // new enrollment weight
225        double enrlWeight = getEnrollmentWeight(assignment, course, enrollment.getRequest());
226        
227        // above limit -> conflict
228        return (enrlWeight > course.getLimit() + sNominalWeight);
229    }
230    
231    @Override
232    public String toString() {
233        return "CourseLimit";
234    }
235
236}