    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 * @author  Tomáš Müller
    034 * @version IFS 1.3 (Iterative Forward Search)<br>
    035 *          Copyright (C) 2014 Tomáš Müller<br>
    036 *          <a href="mailto:muller@unitime.org">muller@unitime.org</a><br>
    037 *          <a href="http://muller.unitime.org">http://muller.unitime.org</a><br>
    038 * <br>
    039 *          This library is free software; you can redistribute it and/or modify
    040 *          it under the terms of the GNU Lesser General Public License as
    041 *          published by the Free Software Foundation; either version 3 of the
    042 *          License, or (at your option) any later version. <br>
    043 * <br>
    044 *          This library is distributed in the hope that it will be useful, but
    045 *          WITHOUT ANY WARRANTY; without even the implied warranty of
    046 *          MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
    047 *          Lesser General Public License for more details. <br>
    048 * <br>
    049 *          You should have received a copy of the GNU Lesser General Public
    050 *          License along with this library; if not see
    051 *          <a href='http://www.gnu.org/licenses/'>http://www.gnu.org/licenses/</a>.
    052 * @param <V> Variable
    053 * @param <T> Value
    054 */
    055public class RandomSwapMove<V extends Variable<V, T>, T extends Value<V, T>> implements NeighbourSelection<V, T>, HillClimberSelection {
    056    protected int iMaxAttempts = 3;
    057    protected boolean iHC = false;
    058    protected int iTimeLimit = 200;
    059
    060    public RandomSwapMove(DataProperties config) {
    061        iMaxAttempts = config.getPropertyInt("RandomSwap.MaxAttempts", iMaxAttempts);
    062        iTimeLimit = config.getPropertyInt("RandomSwap.TimeLimit", iTimeLimit);
    063    }
    064
    065    @Override
    066    public void setHcMode(boolean hcMode) {
    067        iHC = hcMode;
    068    }
    069
    070    @Override
    071    public void init(Solver<V, T> solver) {
    072    }
    073
    074    @Override
    075    public Neighbour<V, T> selectNeighbour(Solution<V, T> solution) {
    076        Model<V, T> model = solution.getModel();
    077        Assignment<V, T> assignment = solution.getAssignment();
    078        double total = model.getTotalValue(assignment);
    079        int varIdx = ToolBox.random(model.variables().size());
    080        for (int i = 0; i < model.variables().size(); i++) {
    081            V variable = model.variables().get((i + varIdx) % model.variables().size());
    082            List<T> values = variable.values(solution.getAssignment());
    083            if (values.isEmpty()) continue;
    084            int valIdx = ToolBox.random(values.size());
    085            T old = variable.getAssignment(assignment);
    086
    087            Lock lock = solution.getLock().writeLock();
    088            lock.lock();
    089            try {
    090                int attempts = 0;
    091                long startTime = JProf.currentTimeMillis();
    092                for (int j = 0; j < values.size(); j++) {
    093                    T value = values.get((j + valIdx) % values.size());
    094                    if (value.equals(old)) continue;
    095
    096                    Set<T> conflicts = model.conflictValues(assignment, value);
    097                    if (conflicts.contains(value)) continue;
    098                    if (conflicts.isEmpty()) {
    099                        SimpleNeighbour<V, T> n = new SimpleNeighbour<V, T>(variable, value);
    100                        if (!iHC || n.value(assignment) <= 0) return n;
    101                        else continue;
    102                    }
    103
    104                    Map<V, T> assignments = new HashMap<V, T>();
    105                    assignments.put(variable, value);
    106
    107                    for (T conflict: conflicts)
    108                        assignment.unassign(solution.getIteration(), conflict.variable());
    109                    assignment.assign(solution.getIteration(), value);
    110
    111                    Double v = resolve(solution, total, startTime, assignments, new ArrayList<T>(conflicts), 0);
    112                    if (!conflicts.isEmpty())
    113                        attempts ++;
    114
    115                    assignment.unassign(solution.getIteration(), variable);
    116                    for (T conflict: conflicts)
    117                        assignment.assign(solution.getIteration(), conflict);
    118                    if (old != null) assignment.assign(solution.getIteration(), old);
    119
    120                    if (v != null)
    121                        return new SwapNeighbour(assignments.values(), old == null ? -1 : v);
    122
    123                    if (attempts >= iMaxAttempts) break;
    124                }
    125            } finally {
    126                lock.unlock();
    127            }
    128        }
    129        return null;
    130    }
    131
    132    /**
    133     * Return true if the time limit was reached, number of attempts are limited to 1 in such a case.
    134     * @param startTime start time
    135     * @return true if the given time limit was reached
    136     */
    137    protected boolean isTimeLimitReached(long startTime) {
    138        return iTimeLimit > 0 && (JProf.currentTimeMillis() - startTime) > iTimeLimit;
    139    }
    140
    141    /**
    142     * Try to resolve given conflicts. For each conflicting variable it tries to find a
    143     * value with no conflict that is compatible with some other assignment
    144     * of the other conflicting variables.
    145     * @param solution current solution
    146     * @param total original value of the current solution
    147     * @param startTime starting time
    148     * @param assignments re-assignments to be made
    149     * @param conflicts list of conflicts to resolve
    150     * @param index index in the list of conflicts
    151     * @return value of the modified solution, null if cannot be resolved
    152     */
    153    protected Double resolve(Solution<V, T> solution, double total, long startTime, Map<V, T> assignments, List<T> conflicts, int index) {
    154        Assignment<V, T> assignment = solution.getAssignment();
    155
    156        if (index == conflicts.size()) return solution.getModel().getTotalValue(assignment) - total;
    157        T conflict = conflicts.get(index);
    158        V variable = conflict.variable();
    159
    160        List<T> values = variable.values(solution.getAssignment());
    161        if (values.isEmpty()) return null;
    162
    163        int valIdx = ToolBox.random(values.size());
    164        int attempts = 0;
    165        for (int i = 0; i < values.size(); i++) {
    166            T value = values.get((i + valIdx) % values.size());
    167            if (value.equals(conflict) || solution.getModel().inConflict(assignment, value)) continue;
    168
    169            assignment.assign(solution.getIteration(), value);
    170            Double v = resolve(solution, total, startTime, assignments, conflicts, 1 + index);
    171            assignment.unassign(solution.getIteration(), variable);
    172            attempts ++;
    173
    174            if (v != null && (!iHC || v <= 0)) {
    175                assignments.put(variable, value);
    176                return v;
    177            }
    178            if (attempts >= iMaxAttempts || isTimeLimitReached(startTime)) break;
    179        }
    180
    181        return null;
    182    }
    183
    184    public class SwapNeighbour implements Neighbour<V, T> {
    185        private double iValue = 0;
    186        private Collection<T> iAssignments = null;
    187
    188        public SwapNeighbour(Collection<T> assignments, double value) {
    189            iAssignments = assignments; iValue = value;
    190        }
    191
    192        @Override
    193        public double value(Assignment<V, T> assignment) {
    194            return iValue;
    195        }
    196
    197        @Override
    198        public void assign(Assignment<V, T> assignment, long iteration) {
    199            for (T value: iAssignments)
    200                assignment.unassign(iteration, value.variable(), value);
    201            for (T value: iAssignments)
    202                assignment.assign(iteration, value);
    203        }
    204
    205        @Override
    206        public String toString() {
    207            StringBuffer sb = new StringBuffer("Swap{" + iValue + ": ");
    208            for (Iterator<T> i = iAssignments.iterator(); i.hasNext(); ) {
    209                T p = i.next();
    210                sb.append("\n    " + p.variable().getName() + " " + p.getName() + (i.hasNext() ? "," : ""));
    211            }
    212            sb.append("}");
    213            return sb.toString();
    214        }
    215
    216        @Override
    217        public Map<V, T> assignments() {
    218            Map<V, T> ret = new HashMap<V, T>();
    219            for (T value: iAssignments)
    220                ret.put(value.variable(), value);
    221            return ret;
    222        }
    223    }
    224}