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.model.Config;
012import org.cpsolver.studentsct.model.Enrollment;
013import org.cpsolver.studentsct.model.Request;
014
015
016/**
017 * Configuration limit constraint. This global constraint ensures that a limit of each
018 * configuration is not exceeded. This means that the total sum of weights of course
019 * requests (see {@link Request#getWeight()}) enrolled into a configuration is below
020 * the configuration's limit (see {@link Config#getLimit()}).
021 * 
022 * <br>
023 * <br>
024 * Configurations with negative limit are considered unlimited, and therefore
025 * completely ignored by this constraint.
026 * 
027 * <br>
028 * <br>
029 * Parameters:
030 * <table border='1' summary='Related Solver Parameters'>
031 * <tr>
032 * <th>Parameter</th>
033 * <th>Type</th>
034 * <th>Comment</th>
035 * </tr>
036 * <tr>
037 * <td>ConfigLimit.PreferDummyStudents</td>
038 * <td>{@link Boolean}</td>
039 * <td>If true, requests of dummy (last-like) students are preferred to be
040 * selected as conflicting.</td>
041 * </tr>
042 * </table>
043 * <br>
044 * <br>
045 * 
046 * @version StudentSct 1.3 (Student Sectioning)<br>
047 *          Copyright (C) 2007 - 2014 Tomas Muller<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 ConfigLimit extends GlobalConstraint<Request, Enrollment> {
066    
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 ConfigLimit(DataProperties cfg) {
077        super();
078        iPreferDummyStudents = cfg.getPropertyBoolean("ConfigLimit.PreferDummyStudents", false);
079    }
080
081
082    /**
083     * Enrollment weight of a config 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 configs 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 config is changed to a small nominal weight.
088     * 
089     * @param assignment current assignment
090     * @param config
091     *            a config 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, Config config, Request request) {
098        return config.getEnrollmentWeight(assignment, request) + request.getWeight() - Math.max(config.getMaxEnrollmentWeight(assignment), request.getWeight()) + sNominalWeight;
099    }
100
101    /**
102     * A given enrollment is conflicting, if the config's enrollment
103     * (computed by {@link ConfigLimit#getEnrollmentWeight(Assignment, Config, 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 (enrollment.getReservation() != null && enrollment.getReservation().canBatchAssignOverLimit())
118            return;
119        
120        // enrollment's config
121        Config config = enrollment.getConfig();
122
123        // exclude free time requests
124        if (config == null)
125            return;
126
127        // exclude empty enrollmens
128        if (enrollment.getSections() == null || enrollment.getSections().isEmpty())
129            return;
130
131        // unlimited config
132        if (config.getLimit() < 0)
133            return;
134        
135        // new enrollment weight
136        double enrlWeight = getEnrollmentWeight(assignment, config, enrollment.getRequest());
137
138        // below limit -> ok
139        if (enrlWeight <= config.getLimit())
140            return;
141
142        // above limit -> compute adepts (current assignments that are not
143        // yet conflicting)
144        // exclude all conflicts as well
145        List<Enrollment> adepts = new ArrayList<Enrollment>(config.getEnrollments(assignment).size());
146        for (Enrollment e : config.getEnrollments(assignment)) {
147            if (e.getRequest().equals(enrollment.getRequest()))
148                continue;
149            if (e.getReservation() != null && e.getReservation().canBatchAssignOverLimit())
150                continue;
151            if (conflicts.contains(e))
152                enrlWeight -= e.getRequest().getWeight();
153            else
154                adepts.add(e);
155        }
156
157        // while above limit -> pick an adept and make it conflicting
158        while (enrlWeight > config.getLimit()) {
159            if (adepts.isEmpty()) {
160                // no adepts -> enrollment cannot be assigned
161                conflicts.add(enrollment);
162                return;
163            }
164            
165            // pick adept (prefer dummy students & students w/o reservation), decrease enrollment
166            // weight, make conflict
167            List<Enrollment> best = new ArrayList<Enrollment>();
168            boolean bestDummy = false;
169            double bestValue = 0;
170            boolean bestRes = true;
171            for (Enrollment adept: adepts) {
172                boolean dummy = adept.getStudent().isDummy();
173                double value = adept.toDouble(assignment, false);
174                boolean res = (adept.getReservation() != null);
175                
176                if (iPreferDummyStudents && dummy != bestDummy) {
177                    if (dummy) {
178                        best.clear();
179                        best.add(adept);
180                        bestDummy = dummy;
181                        bestValue = value;
182                        bestRes = res;
183                    }
184                    continue;
185                }
186                
187                if (bestRes != res) {
188                    if (!res) {
189                        best.clear();
190                        best.add(adept);
191                        bestDummy = dummy;
192                        bestValue = value;
193                        bestRes = res;
194                    }
195                    continue;
196                }
197
198                if (best.isEmpty() || value > bestValue) {
199                    if (best.isEmpty()) best.clear();
200                    best.add(adept);
201                    bestDummy = dummy;
202                    bestValue = value;
203                    bestRes = res;
204                } else if (bestValue == value) {
205                    best.add(adept);
206                }
207            }
208            
209            Enrollment conflict = ToolBox.random(best);
210            adepts.remove(conflict);
211            enrlWeight -= conflict.getRequest().getWeight();
212            conflicts.add(conflict);
213        }
214    }
215
216    /**
217     * A given enrollment is conflicting, if the config's enrollment (computed by
218     * {@link ConfigLimit#getEnrollmentWeight(Assignment, Config, Request)}) exceeds the
219     * limit.
220     * 
221     * @param enrollment
222     *            {@link Enrollment} that is being considered
223     * @return true, if the enrollment cannot be assigned without exceeding the limit
224     */
225    @Override
226    public boolean inConflict(Assignment<Request, Enrollment> assignment, Enrollment enrollment) {
227        // check reservation can assign over the limit
228        if (enrollment.getReservation() != null && enrollment.getReservation().canBatchAssignOverLimit())
229            return false;
230
231        // enrollment's config
232        Config config = enrollment.getConfig();
233
234        // exclude free time requests
235        if (config == null)
236            return false;
237        
238        // exclude empty enrollmens
239        if (enrollment.getSections() == null || enrollment.getSections().isEmpty())
240            return false;
241
242        // unlimited config
243        if (config.getLimit() < 0)
244            return false;
245
246        // new enrollment weight
247        double enrlWeight = getEnrollmentWeight(assignment, config, enrollment.getRequest());
248        
249        // above limit -> conflict
250        return (enrlWeight > config.getLimit());
251    }
252    
253    @Override
254    public String toString() {
255        return "ConfigLimit";
256    }
257
258}