001 package net.sf.cpsolver.ifs.dbt;
002
003 import net.sf.cpsolver.ifs.extension.Extension;
004 import net.sf.cpsolver.ifs.heuristics.VariableSelection;
005 import net.sf.cpsolver.ifs.model.Value;
006 import net.sf.cpsolver.ifs.model.Variable;
007 import net.sf.cpsolver.ifs.solution.Solution;
008 import net.sf.cpsolver.ifs.solver.Solver;
009 import net.sf.cpsolver.ifs.util.DataProperties;
010
011 /**
012 * Selection of a variable for dynamic backtracking. <br>
013 * <br>
014 * <li>Returns null if all variables are assigned. <li>Checks if there is a
015 * varaible with all values marked as nogood (and pick it if there is any). <li>
016 * Returns the first unassigned variable. <br>
017 * <br>
018 * This IFS solver variable selection heuristics is to be used only in case of
019 * dynamic backtracking and it has no parameters.
020 *
021 *
022 * @version IFS 1.2 (Iterative Forward Search)<br>
023 * Copyright (C) 2006 - 2010 Tomas Muller<br>
024 * <a href="mailto:muller@unitime.org">muller@unitime.org</a><br>
025 * <a href="http://muller.unitime.org">http://muller.unitime.org</a><br>
026 * <br>
027 * This library is free software; you can redistribute it and/or modify
028 * it under the terms of the GNU Lesser General Public License as
029 * published by the Free Software Foundation; either version 3 of the
030 * License, or (at your option) any later version. <br>
031 * <br>
032 * This library is distributed in the hope that it will be useful, but
033 * WITHOUT ANY WARRANTY; without even the implied warranty of
034 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
035 * Lesser General Public License for more details. <br>
036 * <br>
037 * You should have received a copy of the GNU Lesser General Public
038 * License along with this library; if not see
039 * <a href='http://www.gnu.org/licenses/'>http://www.gnu.org/licenses/</a>.
040 */
041 public class DbtVariableSelection<V extends Variable<V, T>, T extends Value<V, T>> implements VariableSelection<V, T> {
042 private DbtPropagation<V, T> iProp = null;
043
044 public DbtVariableSelection(DataProperties properties) {
045 }
046
047 /**
048 * Heuristics initialization
049 *
050 * @see VariableSelection#init(Solver)
051 */
052 @Override
053 public void init(Solver<V, T> solver) {
054 for (Extension<V, T> extension : solver.getExtensions()) {
055 if (extension instanceof DbtPropagation<?, ?>) {
056 iProp = (DbtPropagation<V, T>) extension;
057 }
058 }
059 }
060
061 /**
062 * Variable selection
063 *
064 * @see VariableSelection#selectVariable(Solution)
065 */
066 @Override
067 public V selectVariable(Solution<V, T> solution) {
068 if (solution.getModel().nrUnassignedVariables() == 0) {
069 return null;
070 }
071 if (iProp != null) {
072 for (V variable : solution.getModel().unassignedVariables()) {
073 if (iProp.goodValues(variable).isEmpty()) {
074 return variable;
075 }
076 }
077 }
078 return solution.getModel().unassignedVariables().iterator().next();
079 }
080
081 }