001 package net.sf.cpsolver.studentsct.constraint;
002
003 import java.util.ArrayList;
004 import java.util.List;
005 import java.util.Set;
006
007 import net.sf.cpsolver.ifs.model.GlobalConstraint;
008 import net.sf.cpsolver.ifs.util.DataProperties;
009 import net.sf.cpsolver.ifs.util.ToolBox;
010 import net.sf.cpsolver.studentsct.StudentSectioningModel;
011 import net.sf.cpsolver.studentsct.model.Course;
012 import net.sf.cpsolver.studentsct.model.Enrollment;
013 import net.sf.cpsolver.studentsct.model.Request;
014
015 /**
016 * Course limit constraint. This global constraint ensures that a limit of each
017 * course is not exceeded. This means that the total sum of weights of course
018 * requests (see {@link Request#getWeight()}) enrolled into a course is below
019 * the course's limit (see {@link Course#getLimit()}).
020 *
021 * <br>
022 * <br>
023 * Sections with negative limit are considered unlimited, and therefore
024 * completely ignored by this constraint.
025 *
026 * <br>
027 * <br>
028 * Parameters:
029 * <table border='1'>
030 * <tr>
031 * <th>Parameter</th>
032 * <th>Type</th>
033 * <th>Comment</th>
034 * </tr>
035 * <tr>
036 * <td>CourseLimit.PreferDummyStudents</td>
037 * <td>{@link Boolean}</td>
038 * <td>If true, requests of dummy (last-like) students are preferred to be
039 * selected as conflicting.</td>
040 * </tr>
041 * </table>
042 * <br>
043 * <br>
044 *
045 * @version StudentSct 1.2 (Student Sectioning)<br>
046 * Copyright (C) 2007 - 2010 Tomas Muller<br>
047 * <a href="mailto:muller@unitime.org">muller@unitime.org</a><br>
048 * <a href="http://muller.unitime.org">http://muller.unitime.org</a><br>
049 * <br>
050 * This library is free software; you can redistribute it and/or modify
051 * it under the terms of the GNU Lesser General Public License as
052 * published by the Free Software Foundation; either version 3 of the
053 * License, or (at your option) any later version. <br>
054 * <br>
055 * This library is distributed in the hope that it will be useful, but
056 * WITHOUT ANY WARRANTY; without even the implied warranty of
057 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
058 * Lesser General Public License for more details. <br>
059 * <br>
060 * You should have received a copy of the GNU Lesser General Public
061 * License along with this library; if not see
062 * <a href='http://www.gnu.org/licenses/'>http://www.gnu.org/licenses/</a>.
063 */
064 public class CourseLimit extends GlobalConstraint<Request, Enrollment> {
065 private boolean iPreferDummyStudents = false;
066
067 /**
068 * Constructor
069 *
070 * @param cfg
071 * solver configuration
072 */
073 public CourseLimit(DataProperties cfg) {
074 super();
075 iPreferDummyStudents = cfg.getPropertyBoolean("CourseLimit.PreferDummyStudents", false);
076 }
077
078
079 /**
080 * Enrollment weight of a course if the given request is assigned.
081 *
082 * @param course
083 * a course that is of concern
084 * @param request
085 * a request of a student to be assigned containing the given
086 * section
087 * @return section's new weight
088 */
089 public static double getEnrollmentWeight(Course course, Request request) {
090 return course.getEnrollmentWeight(request) + request.getWeight();
091 }
092
093 /**
094 * A given enrollment is conflicting, if the course's enrollment
095 * (computed by {@link CourseLimit#getEnrollmentWeight(Course, Request)})
096 * exceeds the limit. <br>
097 * If the limit is breached, one or more existing enrollments are
098 * (randomly) selected as conflicting until the overall weight is under the
099 * limit.
100 *
101 * @param enrollment
102 * {@link Enrollment} that is being considered
103 * @param conflicts
104 * all computed conflicting requests are added into this set
105 */
106 @Override
107 public void computeConflicts(Enrollment enrollment, Set<Enrollment> conflicts) {
108 // check reservation can assign over the limit
109 if (((StudentSectioningModel)getModel()).getReservationCanAssignOverTheLimit() &&
110 enrollment.getReservation() != null && enrollment.getReservation().canAssignOverLimit())
111 return;
112
113 // enrollment's course
114 Course course = enrollment.getCourse();
115
116 // exclude free time requests
117 if (course == null)
118 return;
119
120 // unlimited course
121 if (course.getLimit() < 0)
122 return;
123
124 // new enrollment weight
125 double enrlWeight = getEnrollmentWeight(course, enrollment.getRequest());
126
127 // below limit -> ok
128 if (enrlWeight <= course.getLimit())
129 return;
130
131 // above limit -> compute adepts (current assignments that are not
132 // yet conflicting)
133 // exclude all conflicts as well
134 List<Enrollment> adepts = new ArrayList<Enrollment>(course.getEnrollments().size());
135 for (Enrollment e : course.getEnrollments()) {
136 if (e.getRequest().equals(enrollment.getRequest()))
137 continue;
138 if (conflicts.contains(e))
139 enrlWeight -= e.getRequest().getWeight();
140 else
141 adepts.add(e);
142 }
143
144 // while above limit -> pick an adept and make it conflicting
145 while (enrlWeight > course.getLimit()) {
146 if (adepts.isEmpty()) {
147 // no adepts -> enrollment cannot be assigned
148 conflicts.add(enrollment);
149 break;
150 }
151
152 // pick adept (prefer dummy students), decrease unreserved space,
153 // make conflict
154 List<Enrollment> best = new ArrayList<Enrollment>();
155 boolean bestDummy = false;
156 double bestValue = 0;
157 for (Enrollment adept: adepts) {
158 boolean dummy = adept.getStudent().isDummy();
159 double value = adept.toDouble(false);
160
161 if (iPreferDummyStudents && dummy != bestDummy) {
162 if (dummy) {
163 best.clear();
164 best.add(adept);
165 bestDummy = dummy;
166 bestValue = value;
167 }
168 continue;
169 }
170
171 if (best.isEmpty() || value > bestValue) {
172 if (best.isEmpty()) best.clear();
173 best.add(adept);
174 bestDummy = dummy;
175 bestValue = value;
176 } else if (bestValue == value) {
177 best.add(adept);
178 }
179 }
180
181 Enrollment conflict = ToolBox.random(best);
182 adepts.remove(conflict);
183 enrlWeight -= conflict.getRequest().getWeight();
184 conflicts.add(conflict);
185 }
186 }
187
188 /**
189 * A given enrollment is conflicting, if the course's enrollment (computed by
190 * {@link CourseLimit#getEnrollmentWeight(Course, Request)}) exceeds the
191 * limit.
192 *
193 * @param enrollment
194 * {@link Enrollment} that is being considered
195 * @return true, if the enrollment cannot be assigned without exceeding the limit
196 */
197 @Override
198 public boolean inConflict(Enrollment enrollment) {
199 // check reservation can assign over the limit
200 if (((StudentSectioningModel)getModel()).getReservationCanAssignOverTheLimit() &&
201 enrollment.getReservation() != null && enrollment.getReservation().canAssignOverLimit())
202 return false;
203
204 // enrollment's course
205 Course course = enrollment.getCourse();
206
207 // exclude free time requests
208 if (course == null)
209 return false;
210
211 // unlimited course
212 if (course.getLimit() < 0)
213 return false;
214
215
216 // new enrollment weight
217 double enrlWeight = getEnrollmentWeight(course, enrollment.getRequest());
218
219 // above limit -> conflict
220 return (enrlWeight > course.getLimit());
221 }
222
223 @Override
224 public String toString() {
225 return "CourseLimit";
226 }
227
228 }