001package org.cpsolver.studentsct.heuristics; 002 003import java.util.ArrayList; 004import java.util.Iterator; 005 006import org.cpsolver.ifs.assignment.Assignment; 007import org.cpsolver.ifs.heuristics.BacktrackNeighbourSelection; 008import org.cpsolver.ifs.util.DataProperties; 009import org.cpsolver.studentsct.model.CourseRequest; 010import org.cpsolver.studentsct.model.Enrollment; 011import org.cpsolver.studentsct.model.Request; 012 013 014/** 015 * Randomized backtracking-based neighbour selection. This class extends 016 * {@link RandomizedBacktrackNeighbourSelection}, however, only a randomly 017 * selected subset of enrollments of each request is considered ( 018 * {@link CourseRequest#computeRandomEnrollments(Assignment, int)} with the given limit is 019 * used). 020 * 021 * <br> 022 * <br> 023 * Parameters: <br> 024 * <table border='1' summary='Related Solver Parameters'> 025 * <tr> 026 * <th>Parameter</th> 027 * <th>Type</th> 028 * <th>Comment</th> 029 * </tr> 030 * <tr> 031 * <td>Neighbour.MaxValues</td> 032 * <td>{@link Integer}</td> 033 * <td>Limit on the number of enrollments to be visited of each 034 * {@link CourseRequest}.</td> 035 * </tr> 036 * </table> 037 * <br> 038 * <br> 039 * 040 * @version StudentSct 1.3 (Student Sectioning)<br> 041 * Copyright (C) 2007 - 2014 Tomas Muller<br> 042 * <a href="mailto:muller@unitime.org">muller@unitime.org</a><br> 043 * <a href="http://muller.unitime.org">http://muller.unitime.org</a><br> 044 * <br> 045 * This library is free software; you can redistribute it and/or modify 046 * it under the terms of the GNU Lesser General Public License as 047 * published by the Free Software Foundation; either version 3 of the 048 * License, or (at your option) any later version. <br> 049 * <br> 050 * This library is distributed in the hope that it will be useful, but 051 * WITHOUT ANY WARRANTY; without even the implied warranty of 052 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU 053 * Lesser General Public License for more details. <br> 054 * <br> 055 * You should have received a copy of the GNU Lesser General Public 056 * License along with this library; if not see 057 * <a href='http://www.gnu.org/licenses/'>http://www.gnu.org/licenses/</a>. 058 */ 059public class RandomizedBacktrackNeighbourSelection extends BacktrackNeighbourSelection<Request, Enrollment> { 060 private int iMaxValues = 100; 061 062 /** 063 * Constructor 064 * 065 * @param properties 066 * configuration 067 * @throws Exception thrown when the initialization fails 068 */ 069 public RandomizedBacktrackNeighbourSelection(DataProperties properties) throws Exception { 070 super(properties); 071 iMaxValues = properties.getPropertyInt("Neighbour.MaxValues", iMaxValues); 072 } 073 074 /** 075 * List of values of a variable. 076 * {@link CourseRequest#computeRandomEnrollments(Assignment, int)} with the provided 077 * limit is used for a {@link CourseRequest}. 078 */ 079 @Override 080 protected Iterator<Enrollment> values(BacktrackNeighbourSelection<Request, Enrollment>.BacktrackNeighbourSelectionContext context, Request variable) { 081 if (iMaxValues > 0 && variable instanceof CourseRequest) { 082 return new ArrayList<Enrollment>(((CourseRequest) variable).computeRandomEnrollments(context.getAssignment(), iMaxValues)).iterator(); 083 } 084 return variable.computeEnrollments(context.getAssignment()).iterator(); 085 } 086}