001package org.cpsolver.studentsct.heuristics.selection;
002
003import java.util.ArrayList;
004import java.util.Collections;
005import java.util.HashSet;
006import java.util.Iterator;
007import java.util.LinkedList;
008import java.util.List;
009import java.util.Queue;
010import java.util.Set;
011
012import org.cpsolver.ifs.assignment.Assignment;
013import org.cpsolver.ifs.heuristics.BacktrackNeighbourSelection;
014import org.cpsolver.ifs.heuristics.NeighbourSelection;
015import org.cpsolver.ifs.heuristics.RouletteWheelSelection;
016import org.cpsolver.ifs.model.Neighbour;
017import org.cpsolver.ifs.model.SimpleNeighbour;
018import org.cpsolver.ifs.solution.Solution;
019import org.cpsolver.ifs.solver.Solver;
020import org.cpsolver.ifs.util.DataProperties;
021import org.cpsolver.ifs.util.Progress;
022import org.cpsolver.ifs.util.ToolBox;
023import org.cpsolver.studentsct.StudentSectioningModel;
024import org.cpsolver.studentsct.model.Course;
025import org.cpsolver.studentsct.model.CourseRequest;
026import org.cpsolver.studentsct.model.Enrollment;
027import org.cpsolver.studentsct.model.Offering;
028import org.cpsolver.studentsct.model.Request;
029import org.cpsolver.studentsct.model.RequestGroup;
030import org.cpsolver.studentsct.model.Section;
031import org.cpsolver.studentsct.model.Subpart;
032
033/**
034 * Shuffle students along request groups. This selection tries to improve the
035 * ability to keep students of the same request group together by moving students
036 * of a request group that are spread over multiple sections into a single section
037 * or into a fewer number of sections.
038 * 
039 * @version StudentSct 1.3 (Student Sectioning)<br>
040 *          Copyright (C) 2007 - 2014 Tomáš Müller<br>
041 *          <a href="mailto:muller@unitime.org">muller@unitime.org</a><br>
042 *          <a href="http://muller.unitime.org">http://muller.unitime.org</a><br>
043 * <br>
044 *          This library is free software; you can redistribute it and/or modify
045 *          it under the terms of the GNU Lesser General Public License as
046 *          published by the Free Software Foundation; either version 3 of the
047 *          License, or (at your option) any later version. <br>
048 * <br>
049 *          This library is distributed in the hope that it will be useful, but
050 *          WITHOUT ANY WARRANTY; without even the implied warranty of
051 *          MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
052 *          Lesser General Public License for more details. <br>
053 * <br>
054 *          You should have received a copy of the GNU Lesser General Public
055 *          License along with this library; if not see
056 *          <a href='http://www.gnu.org/licenses/'>http://www.gnu.org/licenses/</a>.
057 */
058public class ShuffleStudentsSelection implements NeighbourSelection<Request, Enrollment> {
059    private Queue<Shuffle> iQueue = null;
060    private ShuffleBacktrackNeighbourSelection iBacktrack;
061    
062    /**
063     * Constructor
064     * @param properties the selection has no properties at the moment 
065     */
066    public ShuffleStudentsSelection(DataProperties properties) {
067    }
068
069    @Override
070    public void init(Solver<Request, Enrollment> solver) {
071        StudentSectioningModel model = (StudentSectioningModel)solver.currentSolution().getModel();
072        iQueue = new LinkedList<Shuffle>();
073        Assignment<Request, Enrollment> assignment = solver.currentSolution().getAssignment();
074        // Check all request groups that have a spread < 1.0 
075        RouletteWheelSelection<RequestGroup> groups = new RouletteWheelSelection<RequestGroup>();
076        for (Offering offering: model.getOfferings()) {
077            for (Course course: offering.getCourses()) {
078                for (RequestGroup group: course.getRequestGroups()) {
079                    double spread = group.getAverageSpread(solver.currentSolution().getAssignment()); 
080                    if (spread >= 1.0) continue;
081                    groups.add(group, 1.0 - spread);
082                }
083            }
084        }
085        // If there are some, pick one randomly (using roulette wheel selection)
086        if (groups.hasMoreElements()) {
087            RequestGroup group = groups.nextElement();
088            RouletteWheelSelection<Subpart> subparts = new RouletteWheelSelection<Subpart>();
089            for (CourseRequest cr: group.getRequests()) {
090                Enrollment e = assignment.getValue(cr);
091                if (e != null)
092                    for (Section section: e.getSections())
093                        if (group.getSectionSpread(assignment, section) < 1.0)
094                            subparts.addExisting(section.getSubpart(), 1.0);
095            }
096            if (subparts.hasMoreElements()) {
097                // Pick a subpart that has sections with a section spread < 1.0
098                Subpart subpart = subparts.nextElement();
099                RouletteWheelSelection<Section> sections = new RouletteWheelSelection<Section>();
100                section: for (Section section: subpart.getSections()) {
101                    // Only take sections that all requests can use
102                    for (CourseRequest cr: group.getRequests()) {
103                        boolean match = false;
104                        for (Enrollment e: cr.values(assignment))
105                            if (e.getSections().contains(section)) { match = true; break; }
106                        if (!match) continue section;
107                    }
108                    // Take sections with conflicts with lower probability
109                    int nrConflicts = 0;
110                    if (!section.isAllowOverlap())
111                        requests: for (CourseRequest cr: group.getRequests()) {
112                            for (Request r: cr.getStudent().getRequests()) {
113                                if (r.equals(cr)) continue;
114                                Enrollment e = assignment.getValue(r);
115                                if (e != null && !e.isAllowOverlap() && section.isOverlapping(e.getSections())) {
116                                    nrConflicts++; continue requests;
117                                }
118                            }
119                        }
120                    sections.add(section, 1 + group.getRequests().size() - nrConflicts);
121                }
122                Set<Section> filter = new HashSet<Section>(); double space = 0.0;
123                // Pick enough sections
124                while (sections.hasMoreElements()) {
125                    Section section = sections.nextElement();
126                    if (filter.add(section)) {
127                        if (section.getLimit() < 0) break;
128                        space += section.getLimit();
129                    }
130                    if (space >= group.getTotalWeight()) break;
131                }
132                // Add all requests that should be moved into the queue
133                for (CourseRequest cr: group.getRequests()) {
134                    Shuffle shuffle = new Shuffle(group, cr, filter);
135                    Enrollment e = assignment.getValue(cr);
136                    if (e != null && shuffle.matchFilter(e)) continue;
137                    iQueue.add(shuffle);
138                }
139            } else {
140                // No subpart -> no section filter
141                for (CourseRequest cr: group.getRequests())
142                    iQueue.add(new Shuffle(group, cr, null));
143            }
144        }
145        // Shuffle the queue
146        Collections.shuffle((LinkedList<Shuffle>)iQueue);
147        // Initialize the backtrack selection, if needed
148        if (iBacktrack == null) {
149            try {
150                iBacktrack = new ShuffleBacktrackNeighbourSelection(solver.getProperties());
151                iBacktrack.init(solver);
152            } catch (Exception e) {
153                throw new RuntimeException(e.getMessage(), e);
154            }
155        }
156        // Change progress
157        Progress.getInstance(solver.currentSolution().getModel()).setPhase("Shuffling students along request groups...", iQueue.size());
158    }
159
160    @Override
161    public Neighbour<Request, Enrollment> selectNeighbour(Solution<Request, Enrollment> solution) {
162        Shuffle shuffle = null;
163        while ((shuffle = iQueue.poll()) != null) {
164            Progress.getInstance(solution.getModel()).incProgress();
165            // Take an item from the queue, try backtrack first
166            Neighbour<Request, Enrollment> n = iBacktrack.selectNeighbour(solution, shuffle);
167            if (n != null) return n;
168            // If fails, just assign the request randomly and hope for the best
169            List<Enrollment> adepts = new ArrayList<Enrollment>();
170            for (Enrollment e: shuffle.getRequest().values(solution.getAssignment())) {
171                if (shuffle.matchFilter(e)) adepts.add(e);
172            }
173            if (!adepts.isEmpty()) {
174                return new SimpleNeighbour<Request, Enrollment>(shuffle.getRequest(), ToolBox.random(adepts));
175            }
176        }
177        return null;
178    }
179
180    /**
181     * One item to be shuffled
182     */
183    private static class Shuffle {
184        RequestGroup iGroup;
185        CourseRequest iRequest;
186        Set<Section> iFilter;
187        
188        /**
189         * Constructor
190         * @param group selected request group
191         * @param request selected request of a request group
192         * @param filter section filter (if used, only enrollments that contain one of the given sections can be used)
193         */
194        Shuffle(RequestGroup group, CourseRequest request, Set<Section> filter) {
195            iGroup = group;
196            iRequest = request;
197            iFilter = filter;
198        }
199        
200        /**
201         * Selected request group
202         * @return a request group
203         */
204        public CourseRequest getRequest() { return iRequest; }
205        
206        /**
207         * Is there a section filter set?
208         * @return true, if only enrollments with matching sections can be used
209         */
210        public boolean hasFilter() { return iFilter != null && !iFilter.isEmpty(); }
211        
212        /**
213         * Is the given request matching this object?
214         * @param variable a request
215         * @return true if the given variable is a course request for a matching course
216         */
217        public boolean matchRequest(Request variable) {
218            return variable instanceof CourseRequest && ((CourseRequest)variable).getCourses().contains(iGroup.getCourse());
219        }
220        
221        /**
222         * Is the given enrollment matching the section filter
223         * @param e an enrollment
224         * @return true if the enrollment contains at least one section of the filter
225         */
226        public boolean matchFilter(Enrollment e) {
227            if (iFilter == null || iFilter.isEmpty()) return true;
228            for (Section s: e.getSections())
229                if (iFilter.contains(s)) return true;
230            return false;
231        }
232    }
233    
234    /**
235     * A special version of the {@link BacktrackNeighbourSelection} that filters the enrollments with the
236     * provided section filter.
237     *
238     */
239    public static class ShuffleBacktrackNeighbourSelection extends BacktrackNeighbourSelection<Request, Enrollment> {
240
241        /**
242         * Constructor
243         * @param properties configuration
244         * @throws Exception thrown when initialization fails
245         */
246        ShuffleBacktrackNeighbourSelection(DataProperties properties) throws Exception {
247            super(properties);
248            setTimeout(properties.getPropertyInt("Shuffle.BackTrackTimeout", getTimeout()));
249            setDepth(properties.getPropertyInt("Shuffle.BackTrackDepth", getDepth()));
250            setMaxIters(properties.getPropertyInt("Shuffle.BackTrackMaxIters", getMaxIters()));
251        }
252        
253        /**
254         * List of values of the given variable that will be considered (filtered using {@link ShuffleStudentsSelection.Shuffle#matchFilter(Enrollment)} if applicable).
255         * @param context assignment context
256         * @param variable given variable
257         * @return values of the given variable that will be considered
258         */
259        @Override
260        protected Iterator<Enrollment> values(BacktrackNeighbourSelectionContext context, Request variable) {
261            Shuffle shuffle = ((ShuffleBacktrackNeighbourSelectionContext)context).getShuffle();
262            if (shuffle.matchRequest(variable) && shuffle.hasFilter()) {
263                List<Enrollment> values = new ArrayList<Enrollment>();
264                for (Iterator<Enrollment> i = super.values(context, variable); i.hasNext(); ) {
265                    Enrollment e = i.next();
266                    if (shuffle.matchFilter(e)) values.add(e);
267                }
268                return values.iterator();
269            } else {
270                return super.values(context, variable);
271            }
272        }
273        
274        protected Neighbour<Request, Enrollment> selectNeighbour(Solution<Request, Enrollment> solution, Shuffle shuffle) {
275            BacktrackNeighbourSelectionContext context = new ShuffleBacktrackNeighbourSelectionContext(solution, shuffle);
276            selectNeighbour(solution, shuffle.getRequest(), context);
277            return context.getBackTrackNeighbour();
278        }
279        
280        private class ShuffleBacktrackNeighbourSelectionContext extends BacktrackNeighbourSelectionContext {
281            private Shuffle iShuffle = null;
282            
283            private ShuffleBacktrackNeighbourSelectionContext(Solution<Request, Enrollment> solution, Shuffle shuffle) {
284                super(solution);
285                iShuffle = shuffle; 
286            }
287            
288            private Shuffle getShuffle() { return iShuffle; }
289        }
290    }
291
292}