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.studentsct.constraint.ConfigLimit.Adepts;
011import org.cpsolver.studentsct.model.Course;
012import org.cpsolver.studentsct.model.Enrollment;
013import org.cpsolver.studentsct.model.Request;
014
015
016/**
017 * Course limit constraint. This global constraint ensures that a limit of each
018 * course is not exceeded. This means that the total sum of weights of course
019 * requests (see {@link Request#getWeight()}) enrolled into a course is below
020 * the course's limit (see {@link Course#getLimit()}).
021 * 
022 * <br>
023 * <br>
024 * Sections 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'><caption>Related Solver Parameters</caption>
031 * <tr>
032 * <th>Parameter</th>
033 * <th>Type</th>
034 * <th>Comment</th>
035 * </tr>
036 * <tr>
037 * <td>CourseLimit.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 * @author  Tomáš Müller
047 * @version StudentSct 1.3 (Student Sectioning)<br>
048 *          Copyright (C) 2007 - 2014 Tomáš Müller<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    private boolean iPreferPriorityStudents = true;
070
071    /**
072     * Constructor
073     * 
074     * @param cfg
075     *            solver configuration
076     */
077    public CourseLimit(DataProperties cfg) {
078        super();
079        iPreferDummyStudents = cfg.getPropertyBoolean("CourseLimit.PreferDummyStudents", false);
080        iPreferPriorityStudents = cfg.getPropertyBoolean("Sectioning.PriorityStudentsFirstSelection.AllIn", true);
081    }
082
083
084    /**
085     * Enrollment weight of a course if the given request is assigned. In order
086     * to overcome rounding problems with last-like students ( e.g., 5 students
087     * are projected to two sections of limit 2 -- each section can have up to 3
088     * of these last-like students), the weight of the request with the highest
089     * weight in the section is changed to a small nominal weight.
090     * 
091     * @param assignment current assignment
092     * @param course
093     *            a course that is of concern
094     * @param request
095     *            a request of a student to be assigned containing the given
096     *            section
097     * @return section's new weight
098     */
099    public static double getEnrollmentWeight(Assignment<Request, Enrollment> assignment, Course course, Request request) {
100        return course.getEnrollmentWeight(assignment, request) + request.getWeight() - Math.max(course.getMaxEnrollmentWeight(assignment), request.getWeight()) + sNominalWeight;
101    }
102
103    /**
104     * A given enrollment is conflicting, if the course's enrollment
105     * (computed by {@link CourseLimit#getEnrollmentWeight(Assignment, Course, Request)})
106     * exceeds the limit. <br>
107     * If the limit is breached, one or more existing enrollments are
108     * (randomly) selected as conflicting until the overall weight is under the
109     * limit.
110     * 
111     * @param enrollment
112     *            {@link Enrollment} that is being considered
113     * @param conflicts
114     *            all computed conflicting requests are added into this set
115     */
116    @Override
117    public void computeConflicts(Assignment<Request, Enrollment> assignment, Enrollment enrollment, Set<Enrollment> conflicts) {
118        // check reservation can assign over the limit
119        if (enrollment.getReservation() != null && enrollment.getReservation().canBatchAssignOverLimit())
120            return;
121
122        // enrollment's course
123        Course course = enrollment.getCourse();
124
125        // exclude free time requests
126        if (course == null)
127            return;
128        
129        // exclude empty enrollmens
130        if (enrollment.getSections() == null || enrollment.getSections().isEmpty())
131            return;
132
133        // unlimited course
134        if (course.getLimit() < 0)
135            return;
136        
137        // new enrollment weight
138        double enrlWeight = getEnrollmentWeight(assignment, course, enrollment.getRequest());
139
140        // below limit -> ok
141        if (enrlWeight <= course.getLimit())
142            return;
143
144        // above limit -> compute adepts (current assignments that are not
145        // yet conflicting)
146        // exclude all conflicts as well
147        List<Enrollment> adepts = new ArrayList<Enrollment>(course.getEnrollments(assignment).size());
148        for (Enrollment e : course.getEnrollments(assignment)) {
149            if (e.getRequest().equals(enrollment.getRequest()))
150                continue;
151            if (e.getReservation() != null && e.getReservation().canBatchAssignOverLimit())
152                continue;
153            if (conflicts.contains(e))
154                enrlWeight -= e.getRequest().getWeight();
155            else
156                adepts.add(e);
157        }
158
159        // while above limit -> pick an adept and make it conflicting
160        while (enrlWeight > course.getLimit()) {
161            if (adepts.isEmpty()) {
162                // no adepts -> enrollment cannot be assigned
163                conflicts.add(enrollment);
164                break;
165            }
166            
167            // pick adept (prefer dummy students), decrease unreserved space,
168            // make conflict
169            Enrollment conflict = new Adepts(iPreferDummyStudents, iPreferPriorityStudents, adepts, assignment).get();
170            adepts.remove(conflict);
171            enrlWeight -= conflict.getRequest().getWeight();
172            conflicts.add(conflict);
173        }
174    }
175
176    /**
177     * A given enrollment is conflicting, if the course's enrollment (computed by
178     * {@link CourseLimit#getEnrollmentWeight(Assignment, Course, Request)}) exceeds the
179     * limit.
180     * 
181     * @param enrollment
182     *            {@link Enrollment} that is being considered
183     * @return true, if the enrollment cannot be assigned without exceeding the limit
184     */
185    @Override
186    public boolean inConflict(Assignment<Request, Enrollment> assignment, Enrollment enrollment) {
187        // check reservation can assign over the limit
188        if (enrollment.getReservation() != null && enrollment.getReservation().canBatchAssignOverLimit())
189            return false;
190
191        // enrollment's course
192        Course course = enrollment.getCourse();
193
194        // exclude free time requests
195        if (course == null)
196            return false;
197        
198        // exclude empty enrollmens
199        if (enrollment.getSections() == null || enrollment.getSections().isEmpty())
200            return false;
201
202        // unlimited course
203        if (course.getLimit() < 0)
204            return false;
205
206
207        // new enrollment weight
208        double enrlWeight = getEnrollmentWeight(assignment, course, enrollment.getRequest());
209        
210        // above limit -> conflict
211        return (enrlWeight > course.getLimit());
212    }
213    
214    @Override
215    public String toString() {
216        return "CourseLimit";
217    }
218
219}