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.Config;
013import org.cpsolver.studentsct.model.Enrollment;
014import org.cpsolver.studentsct.model.Request;
015
016
017/**
018 * Configuration limit constraint. This global constraint ensures that a limit of each
019 * configuration is not exceeded. This means that the total sum of weights of course
020 * requests (see {@link Request#getWeight()}) enrolled into a configuration is below
021 * the configuration's limit (see {@link Config#getLimit()}).
022 * 
023 * <br>
024 * <br>
025 * Configurations 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>ConfigLimit.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 ConfigLimit extends GlobalConstraint<Request, Enrollment> {
067    
068    private static double sNominalWeight = 0.00001;
069    private boolean iPreferDummyStudents = false;
070
071    /**
072     * Constructor
073     * 
074     * @param cfg
075     *            solver configuration
076     */
077    public ConfigLimit(DataProperties cfg) {
078        super();
079        iPreferDummyStudents = cfg.getPropertyBoolean("ConfigLimit.PreferDummyStudents", false);
080    }
081
082
083    /**
084     * Enrollment weight of a config if the given request is assigned. In order
085     * to overcome rounding problems with last-like students ( e.g., 5 students
086     * are projected to two configs of limit 2 -- each section can have up to 3
087     * of these last-like students), the weight of the request with the highest
088     * weight in the config is changed to a small nominal weight.
089     * 
090     * @param assignment current assignment
091     * @param config
092     *            a config that is of concern
093     * @param request
094     *            a request of a student to be assigned containing the given
095     *            section
096     * @return section's new weight
097     */
098    public static double getEnrollmentWeight(Assignment<Request, Enrollment> assignment, Config config, Request request) {
099        return config.getEnrollmentWeight(assignment, request) + request.getWeight() - Math.max(config.getMaxEnrollmentWeight(assignment), request.getWeight()) + sNominalWeight;
100    }
101
102    /**
103     * A given enrollment is conflicting, if the config's enrollment
104     * (computed by {@link ConfigLimit#getEnrollmentWeight(Assignment, Config, Request)})
105     * exceeds the limit. <br>
106     * If the limit is breached, one or more existing enrollments are
107     * (randomly) selected as conflicting until the overall weight is under the
108     * limit.
109     * 
110     * @param enrollment
111     *            {@link Enrollment} that is being considered
112     * @param conflicts
113     *            all computed conflicting requests are added into this set
114     */
115    @Override
116    public void computeConflicts(Assignment<Request, Enrollment> assignment, Enrollment enrollment, Set<Enrollment> conflicts) {
117        // check reservation can assign over the limit
118        if (((StudentSectioningModel)getModel()).getReservationCanAssignOverTheLimit() &&
119            enrollment.getReservation() != null && enrollment.getReservation().canAssignOverLimit())
120            return;
121        
122        // enrollment's config
123        Config config = enrollment.getConfig();
124
125        // exclude free time requests
126        if (config == null)
127            return;
128        
129
130        // unlimited config
131        if (config.getLimit() < 0)
132            return;
133        
134        // new enrollment weight
135        double enrlWeight = getEnrollmentWeight(assignment, config, enrollment.getRequest());
136
137        // below limit -> ok
138        if (enrlWeight <= config.getLimit())
139            return;
140
141        // above limit -> compute adepts (current assignments that are not
142        // yet conflicting)
143        // exclude all conflicts as well
144        List<Enrollment> adepts = new ArrayList<Enrollment>(config.getEnrollments(assignment).size());
145        for (Enrollment e : config.getEnrollments(assignment)) {
146            if (e.getRequest().equals(enrollment.getRequest()))
147                continue;
148            if (conflicts.contains(e))
149                enrlWeight -= e.getRequest().getWeight();
150            else
151                adepts.add(e);
152        }
153
154        // while above limit -> pick an adept and make it conflicting
155        while (enrlWeight > config.getLimit()) {
156            if (adepts.isEmpty()) {
157                // no adepts -> enrollment cannot be assigned
158                conflicts.add(enrollment);
159                return;
160            }
161            
162            // pick adept (prefer dummy students & students w/o reservation), decrease enrollment
163            // weight, make conflict
164            List<Enrollment> best = new ArrayList<Enrollment>();
165            boolean bestDummy = false;
166            double bestValue = 0;
167            boolean bestRes = true;
168            for (Enrollment adept: adepts) {
169                boolean dummy = adept.getStudent().isDummy();
170                double value = adept.toDouble(assignment, false);
171                boolean res = (adept.getReservation() != null);
172                
173                if (iPreferDummyStudents && dummy != bestDummy) {
174                    if (dummy) {
175                        best.clear();
176                        best.add(adept);
177                        bestDummy = dummy;
178                        bestValue = value;
179                        bestRes = res;
180                    }
181                    continue;
182                }
183                
184                if (bestRes != res) {
185                    if (!res) {
186                        best.clear();
187                        best.add(adept);
188                        bestDummy = dummy;
189                        bestValue = value;
190                        bestRes = res;
191                    }
192                    continue;
193                }
194
195                if (best.isEmpty() || value > bestValue) {
196                    if (best.isEmpty()) best.clear();
197                    best.add(adept);
198                    bestDummy = dummy;
199                    bestValue = value;
200                    bestRes = res;
201                } else if (bestValue == value) {
202                    best.add(adept);
203                }
204            }
205            
206            Enrollment conflict = ToolBox.random(best);
207            adepts.remove(conflict);
208            enrlWeight -= conflict.getRequest().getWeight();
209            conflicts.add(conflict);
210        }
211    }
212
213    /**
214     * A given enrollment is conflicting, if the config's enrollment (computed by
215     * {@link ConfigLimit#getEnrollmentWeight(Assignment, Config, Request)}) exceeds the
216     * limit.
217     * 
218     * @param enrollment
219     *            {@link Enrollment} that is being considered
220     * @return true, if the enrollment cannot be assigned without exceeding the limit
221     */
222    @Override
223    public boolean inConflict(Assignment<Request, Enrollment> assignment, Enrollment enrollment) {
224        // check reservation can assign over the limit
225        if (((StudentSectioningModel)getModel()).getReservationCanAssignOverTheLimit() &&
226            enrollment.getReservation() != null && enrollment.getReservation().canAssignOverLimit())
227            return false;
228
229        // enrollment's config
230        Config config = enrollment.getConfig();
231
232        // exclude free time requests
233        if (config == null)
234            return false;
235
236        // unlimited config
237        if (config.getLimit() < 0)
238            return false;
239
240
241        // new enrollment weight
242        double enrlWeight = getEnrollmentWeight(assignment, config, enrollment.getRequest());
243        
244        // above limit -> conflict
245        return (enrlWeight > config.getLimit());
246    }
247    
248    @Override
249    public String toString() {
250        return "ConfigLimit";
251    }
252
253}