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
128        // unlimited config
129        if (config.getLimit() < 0)
130            return;
131        
132        // new enrollment weight
133        double enrlWeight = getEnrollmentWeight(assignment, config, enrollment.getRequest());
134
135        // below limit -> ok
136        if (enrlWeight <= config.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>(config.getEnrollments(assignment).size());
143        for (Enrollment e : config.getEnrollments(assignment)) {
144            if (e.getRequest().equals(enrollment.getRequest()))
145                continue;
146            if (e.getReservation() != null && e.getReservation().canBatchAssignOverLimit())
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 (enrollment.getReservation() != null && enrollment.getReservation().canBatchAssignOverLimit())
226            return false;
227
228        // enrollment's config
229        Config config = enrollment.getConfig();
230
231        // exclude free time requests
232        if (config == null)
233            return false;
234
235        // unlimited config
236        if (config.getLimit() < 0)
237            return false;
238
239
240        // new enrollment weight
241        double enrlWeight = getEnrollmentWeight(assignment, config, enrollment.getRequest());
242        
243        // above limit -> conflict
244        return (enrlWeight > config.getLimit());
245    }
246    
247    @Override
248    public String toString() {
249        return "ConfigLimit";
250    }
251
252}