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' summary='Related Solver Parameters'>
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 * @version StudentSct 1.3 (Student Sectioning)<br>
047 *          Copyright (C) 2007 - 2014 Tomáš Müller<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 CourseLimit extends GlobalConstraint<Request, Enrollment> {
066    private static double sNominalWeight = 0.00001;
067    private boolean iPreferDummyStudents = false;
068    private boolean iPreferPriorityStudents = true;
069
070    /**
071     * Constructor
072     * 
073     * @param cfg
074     *            solver configuration
075     */
076    public CourseLimit(DataProperties cfg) {
077        super();
078        iPreferDummyStudents = cfg.getPropertyBoolean("CourseLimit.PreferDummyStudents", false);
079        iPreferPriorityStudents = cfg.getPropertyBoolean("Sectioning.PriorityStudentsFirstSelection.AllIn", true);
080    }
081
082
083    /**
084     * Enrollment weight of a course 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 sections 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 section is changed to a small nominal weight.
089     * 
090     * @param assignment current assignment
091     * @param course
092     *            a course 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, Course course, Request request) {
099        return course.getEnrollmentWeight(assignment, request) + request.getWeight() - Math.max(course.getMaxEnrollmentWeight(assignment), request.getWeight()) + sNominalWeight;
100    }
101
102    /**
103     * A given enrollment is conflicting, if the course's enrollment
104     * (computed by {@link CourseLimit#getEnrollmentWeight(Assignment, Course, 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 (enrollment.getReservation() != null && enrollment.getReservation().canBatchAssignOverLimit())
119            return;
120
121        // enrollment's course
122        Course course = enrollment.getCourse();
123
124        // exclude free time requests
125        if (course == null)
126            return;
127        
128        // exclude empty enrollmens
129        if (enrollment.getSections() == null || enrollment.getSections().isEmpty())
130            return;
131
132        // unlimited course
133        if (course.getLimit() < 0)
134            return;
135        
136        // new enrollment weight
137        double enrlWeight = getEnrollmentWeight(assignment, course, enrollment.getRequest());
138
139        // below limit -> ok
140        if (enrlWeight <= course.getLimit())
141            return;
142
143        // above limit -> compute adepts (current assignments that are not
144        // yet conflicting)
145        // exclude all conflicts as well
146        List<Enrollment> adepts = new ArrayList<Enrollment>(course.getEnrollments(assignment).size());
147        for (Enrollment e : course.getEnrollments(assignment)) {
148            if (e.getRequest().equals(enrollment.getRequest()))
149                continue;
150            if (e.getReservation() != null && e.getReservation().canBatchAssignOverLimit())
151                continue;
152            if (conflicts.contains(e))
153                enrlWeight -= e.getRequest().getWeight();
154            else
155                adepts.add(e);
156        }
157
158        // while above limit -> pick an adept and make it conflicting
159        while (enrlWeight > course.getLimit()) {
160            if (adepts.isEmpty()) {
161                // no adepts -> enrollment cannot be assigned
162                conflicts.add(enrollment);
163                break;
164            }
165            
166            // pick adept (prefer dummy students), decrease unreserved space,
167            // make conflict
168            Enrollment conflict = new Adepts(iPreferDummyStudents, iPreferPriorityStudents, adepts, assignment).get();
169            adepts.remove(conflict);
170            enrlWeight -= conflict.getRequest().getWeight();
171            conflicts.add(conflict);
172        }
173    }
174
175    /**
176     * A given enrollment is conflicting, if the course's enrollment (computed by
177     * {@link CourseLimit#getEnrollmentWeight(Assignment, Course, Request)}) exceeds the
178     * limit.
179     * 
180     * @param enrollment
181     *            {@link Enrollment} that is being considered
182     * @return true, if the enrollment cannot be assigned without exceeding the limit
183     */
184    @Override
185    public boolean inConflict(Assignment<Request, Enrollment> assignment, Enrollment enrollment) {
186        // check reservation can assign over the limit
187        if (enrollment.getReservation() != null && enrollment.getReservation().canBatchAssignOverLimit())
188            return false;
189
190        // enrollment's course
191        Course course = enrollment.getCourse();
192
193        // exclude free time requests
194        if (course == null)
195            return false;
196        
197        // exclude empty enrollmens
198        if (enrollment.getSections() == null || enrollment.getSections().isEmpty())
199            return false;
200
201        // unlimited course
202        if (course.getLimit() < 0)
203            return false;
204
205
206        // new enrollment weight
207        double enrlWeight = getEnrollmentWeight(assignment, course, enrollment.getRequest());
208        
209        // above limit -> conflict
210        return (enrlWeight > course.getLimit());
211    }
212    
213    @Override
214    public String toString() {
215        return "CourseLimit";
216    }
217
218}