    001package org.cpsolver.ifs.algorithms.neighbourhoods;
    002
    003import java.util.ArrayList;
    004import java.util.Collection;
    005import java.util.HashMap;
    006import java.util.Iterator;
    007import java.util.List;
    008import java.util.Map;
    009import java.util.Set;
    010import java.util.concurrent.locks.Lock;
    011
    012import org.cpsolver.ifs.assignment.Assignment;
    013import org.cpsolver.ifs.heuristics.NeighbourSelection;
    014import org.cpsolver.ifs.model.Model;
    015import org.cpsolver.ifs.model.Neighbour;
    016import org.cpsolver.ifs.model.SimpleNeighbour;
    017import org.cpsolver.ifs.model.Value;
    018import org.cpsolver.ifs.model.Variable;
    019import org.cpsolver.ifs.solution.Solution;
    020import org.cpsolver.ifs.solver.Solver;
    021import org.cpsolver.ifs.util.DataProperties;
    022import org.cpsolver.ifs.util.JProf;
    023import org.cpsolver.ifs.util.ToolBox;
    024
    025
    026/**
    027 * Try to assign a variable with a new value. A variable is selected randomly, a
    028 * different value is randomly selected for the variable -- the variable is
    029 * assigned with the new value.  If there is a conflict, it tries to resolve these
    030 * conflicts by assigning conflicting variables to other values as well.
    031 * <br>
    032 *
    033 * @version IFS 1.3 (Iterative Forward Search)<br>
    034 *          Copyright (C) 2014 Tomáš Müller<br>
    035 *          <a href="mailto:muller@unitime.org">muller@unitime.org</a><br>
    036 *          <a href="http://muller.unitime.org">http://muller.unitime.org</a><br>
    037 * <br>
    038 *          This library is free software; you can redistribute it and/or modify
    039 *          it under the terms of the GNU Lesser General Public License as
    040 *          published by the Free Software Foundation; either version 3 of the
    041 *          License, or (at your option) any later version. <br>
    042 * <br>
    043 *          This library is distributed in the hope that it will be useful, but
    044 *          WITHOUT ANY WARRANTY; without even the implied warranty of
    045 *          MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
    046 *          Lesser General Public License for more details. <br>
    047 * <br>
    048 *          You should have received a copy of the GNU Lesser General Public
    049 *          License along with this library; if not see
    050 *          <a href='http://www.gnu.org/licenses/'>http://www.gnu.org/licenses/</a>.
    051 * @param <V> Variable
    052 * @param <T> Value
    053 */
    054public class RandomSwapMove<V extends Variable<V, T>, T extends Value<V, T>> implements NeighbourSelection<V, T>, HillClimberSelection {
    055    protected int iMaxAttempts = 3;
    056    protected boolean iHC = false;
    057    protected int iTimeLimit = 200;
    058
    059    public RandomSwapMove(DataProperties config) {
    060        iMaxAttempts = config.getPropertyInt("RandomSwap.MaxAttempts", iMaxAttempts);
    061        iTimeLimit = config.getPropertyInt("RandomSwap.TimeLimit", iTimeLimit);
    062    }
    063
    064    @Override
    065    public void setHcMode(boolean hcMode) {
    066        iHC = hcMode;
    067    }
    068
    069    @Override
    070    public void init(Solver<V, T> solver) {
    071    }
    072
    073    @Override
    074    public Neighbour<V, T> selectNeighbour(Solution<V, T> solution) {
    075        Model<V, T> model = solution.getModel();
    076        Assignment<V, T> assignment = solution.getAssignment();
    077        double total = model.getTotalValue(assignment);
    078        int varIdx = ToolBox.random(model.variables().size());
    079        for (int i = 0; i < model.variables().size(); i++) {
    080            V variable = model.variables().get((i + varIdx) % model.variables().size());
    081            List<T> values = variable.values(solution.getAssignment());
    082            if (values.isEmpty()) continue;
    083            int valIdx = ToolBox.random(values.size());
    084            T old = variable.getAssignment(assignment);
    085
    086            Lock lock = solution.getLock().writeLock();
    087            lock.lock();
    088            try {
    089                int attempts = 0;
    090                long startTime = JProf.currentTimeMillis();
    091                for (int j = 0; j < values.size(); j++) {
    092                    T value = values.get((j + valIdx) % values.size());
    093                    if (value.equals(old)) continue;
    094
    095                    Set<T> conflicts = model.conflictValues(assignment, value);
    096                    if (conflicts.contains(value)) continue;
    097                    if (conflicts.isEmpty()) {
    098                        SimpleNeighbour<V, T> n = new SimpleNeighbour<V, T>(variable, value);
    099                        if (!iHC || n.value(assignment) <= 0) return n;
    100                        else continue;
    101                    }
    102
    103                    Map<V, T> assignments = new HashMap<V, T>();
    104                    assignments.put(variable, value);
    105
    106                    for (T conflict: conflicts)
    107                        assignment.unassign(solution.getIteration(), conflict.variable());
    108                    assignment.assign(solution.getIteration(), value);
    109
    110                    Double v = resolve(solution, total, startTime, assignments, new ArrayList<T>(conflicts), 0);
    111                    if (!conflicts.isEmpty())
    112                        attempts ++;
    113
    114                    assignment.unassign(solution.getIteration(), variable);
    115                    for (T conflict: conflicts)
    116                        assignment.assign(solution.getIteration(), conflict);
    117                    if (old != null) assignment.assign(solution.getIteration(), old);
    118
    119                    if (v != null)
    120                        return new SwapNeighbour(assignments.values(), v);
    121
    122                    if (attempts >= iMaxAttempts) break;
    123                }
    124            } finally {
    125                lock.unlock();
    126            }
    127        }
    128        return null;
    129    }
    130
    131    /**
    132     * Return true if the time limit was reached, number of attempts are limited to 1 in such a case.
    133     * @param startTime start time
    134     * @return true if the given time limit was reached
    135     */
    136    protected boolean isTimeLimitReached(long startTime) {
    137        return iTimeLimit > 0 && (JProf.currentTimeMillis() - startTime) > iTimeLimit;
    138    }
    139
    140    /**
    141     * Try to resolve given conflicts. For each conflicting variable it tries to find a
    142     * value with no conflict that is compatible with some other assignment
    143     * of the other conflicting variables.
    144     * @param solution current solution
    145     * @param total original value of the current solution
    146     * @param startTime starting time
    147     * @param assignments re-assignments to be made
    148     * @param conflicts list of conflicts to resolve
    149     * @param index index in the list of conflicts
    150     * @return value of the modified solution, null if cannot be resolved
    151     */
    152    protected Double resolve(Solution<V, T> solution, double total, long startTime, Map<V, T> assignments, List<T> conflicts, int index) {
    153        Assignment<V, T> assignment = solution.getAssignment();
    154
    155        if (index == conflicts.size()) return solution.getModel().getTotalValue(assignment) - total;
    156        T conflict = conflicts.get(index);
    157        V variable = conflict.variable();
    158
    159        List<T> values = variable.values(solution.getAssignment());
    160        if (values.isEmpty()) return null;
    161
    162        int valIdx = ToolBox.random(values.size());
    163        int attempts = 0;
    164        for (int i = 0; i < values.size(); i++) {
    165            T value = values.get((i + valIdx) % values.size());
    166            if (value.equals(conflict) || solution.getModel().inConflict(assignment, value)) continue;
    167
    168            assignment.assign(solution.getIteration(), value);
    169            Double v = resolve(solution, total, startTime, assignments, conflicts, 1 + index);
    170            assignment.unassign(solution.getIteration(), variable);
    171            attempts ++;
    172
    173            if (v != null && (!iHC || v <= 0)) {
    174                assignments.put(variable, value);
    175                return v;
    176            }
    177            if (attempts >= iMaxAttempts || isTimeLimitReached(startTime)) break;
    178        }
    179
    180        return null;
    181    }
    182
    183    public class SwapNeighbour implements Neighbour<V, T> {
    184        private double iValue = 0;
    185        private Collection<T> iAssignments = null;
    186
    187        public SwapNeighbour(Collection<T> assignments, double value) {
    188            iAssignments = assignments; iValue = value;
    189        }
    190
    191        @Override
    192        public double value(Assignment<V, T> assignment) {
    193            return iValue;
    194        }
    195
    196        @Override
    197        public void assign(Assignment<V, T> assignment, long iteration) {
    198            for (T value: iAssignments)
    199                assignment.unassign(iteration, value.variable(), value);
    200            for (T value: iAssignments)
    201                assignment.assign(iteration, value);
    202        }
    203
    204        @Override
    205        public String toString() {
    206            StringBuffer sb = new StringBuffer("Swap{" + iValue + ": ");
    207            for (Iterator<T> i = iAssignments.iterator(); i.hasNext(); ) {
    208                T p = i.next();
    209                sb.append("\n    " + p.variable().getName() + " " + p.getName() + (i.hasNext() ? "," : ""));
    210            }
    211            sb.append("}");
    212            return sb.toString();
    213        }
    214
    215        @Override
    216        public Map<V, T> assignments() {
    217            Map<V, T> ret = new HashMap<V, T>();
    218            for (T value: iAssignments)
    219                ret.put(value.variable(), value);
    220            return ret;
    221        }
    222    }
    223}