001 package net.sf.cpsolver.ifs.extension;
002
003 import java.util.ArrayList;
004 import java.util.HashSet;
005 import java.util.HashMap;
006 import java.util.List;
007 import java.util.Map;
008 import java.util.Set;
009
010 import net.sf.cpsolver.ifs.model.Constraint;
011 import net.sf.cpsolver.ifs.model.Value;
012 import net.sf.cpsolver.ifs.model.Variable;
013 import net.sf.cpsolver.ifs.solver.Solver;
014 import net.sf.cpsolver.ifs.util.DataProperties;
015
016 /**
017 * Computation of violated initial values (minimal perturbation problem). <br>
018 * <br>
019 * It is using {@link Constraint#isConsistent(Value, Value)} to find out what
020 * initial values (of different variables) cannot be assigned when an arbitrary
021 * value is assigned to a variable. This information is computed in advance,
022 * before the solver is executed. It is used for better estimation of
023 * perturbation penalty (see
024 * {@link net.sf.cpsolver.ifs.perturbations.PerturbationsCounter}) when a value
025 * is to be assigned to a variable.
026 *
027 * @version IFS 1.2 (Iterative Forward Search)<br>
028 * Copyright (C) 2006 - 2010 Tomas Muller<br>
029 * <a href="mailto:muller@unitime.org">muller@unitime.org</a><br>
030 * <a href="http://muller.unitime.org">http://muller.unitime.org</a><br>
031 * <br>
032 * This library is free software; you can redistribute it and/or modify
033 * it under the terms of the GNU Lesser General Public License as
034 * published by the Free Software Foundation; either version 3 of the
035 * License, or (at your option) any later version. <br>
036 * <br>
037 * This library is distributed in the hope that it will be useful, but
038 * WITHOUT ANY WARRANTY; without even the implied warranty of
039 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
040 * Lesser General Public License for more details. <br>
041 * <br>
042 * You should have received a copy of the GNU Lesser General Public
043 * License along with this library; if not see
044 * <a href='http://www.gnu.org/licenses/'>http://www.gnu.org/licenses/</a>.
045 */
046 public class ViolatedInitials<V extends Variable<V, T>, T extends Value<V, T>> extends Extension<V, T> {
047 private static org.apache.log4j.Logger sLogger = org.apache.log4j.Logger.getLogger(ViolatedInitials.class);
048 private Map<T, Set<T>> iViolatedInitials = new HashMap<T, Set<T>>();
049
050 public ViolatedInitials(Solver<V, T> solver, DataProperties properties) {
051 super(solver, properties);
052 }
053
054 /** Compute the violations between any value and all other initial values */
055 public boolean init() {
056 sLogger.info("Computation of violated initials enabled.");
057 for (V variable : getModel().variables()) {
058 if (variable.getInitialAssignment() == null)
059 continue;
060 for (Constraint<V, T> constraint : variable.hardConstraints()) {
061 for (T value : conflictValues(constraint, variable.getInitialAssignment())) {
062 addViolatedInitial(value, variable.getInitialAssignment());
063 }
064 }
065 }
066 return true;
067 }
068
069 /** Initial values that cannot be assigned when the given value is assigned */
070 public Set<T> getViolatedInitials(T value) {
071 return iViolatedInitials.get(value);
072 }
073
074 private void addViolatedInitial(T value, T anotherValue) {
075 Set<T> violations = iViolatedInitials.get(value);
076 if (violations == null) {
077 violations = new HashSet<T>();
078 iViolatedInitials.put(value, violations);
079 }
080 violations.add(anotherValue);
081 }
082
083 private List<T> conflictValues(Constraint<V, T> constraint, T aValue) {
084 List<T> ret = new ArrayList<T>();
085 for (V variable : constraint.variables()) {
086 if (variable.equals(aValue.variable()))
087 continue;
088 if (variable.getAssignment() != null)
089 continue;
090 for (T value : variable.values()) {
091 if (!constraint.isConsistent(aValue, value))
092 ret.add(value);
093 }
094 }
095 return ret;
096 }
097 }