001package net.sf.cpsolver.ifs.extension;
002
003import java.util.ArrayList;
004import java.util.HashSet;
005import java.util.HashMap;
006import java.util.List;
007import java.util.Map;
008import java.util.Set;
009
010import net.sf.cpsolver.ifs.model.Constraint;
011import net.sf.cpsolver.ifs.model.Value;
012import net.sf.cpsolver.ifs.model.Variable;
013import net.sf.cpsolver.ifs.solver.Solver;
014import 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 Tomáš Müller<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 */
046public 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}