    001package org.cpsolver.ifs.heuristics;
    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
    012
    013import org.apache.logging.log4j.Logger;
    014import org.cpsolver.ifs.assignment.Assignment;
    015import org.cpsolver.ifs.assignment.context.AssignmentContext;
    016import org.cpsolver.ifs.constant.ConstantVariable;
    017import org.cpsolver.ifs.extension.ConflictStatistics;
    018import org.cpsolver.ifs.extension.Extension;
    019import org.cpsolver.ifs.model.Model;
    020import org.cpsolver.ifs.model.Neighbour;
    021import org.cpsolver.ifs.model.Value;
    022import org.cpsolver.ifs.model.Variable;
    023import org.cpsolver.ifs.solution.Solution;
    024import org.cpsolver.ifs.solver.Solver;
    025import org.cpsolver.ifs.util.DataProperties;
    026import org.cpsolver.ifs.util.JProf;
    027
    028/**
    029 * Backtracking-based neighbour selection. A best neighbour that is found by a
    030 * backtracking-based algorithm within a limited depth from a selected variable
    031 * is returned. <br>
    032 * <br>
    033 * Parameters: <br>
    034 * <table border='1'><caption>Related Solver Parameters</caption>
    035 * <tr>
    036 * <th>Parameter</th>
    037 * <th>Type</th>
    038 * <th>Comment</th>
    039 * </tr>
    040 * <tr>
    041 * <td>Neighbour.BackTrackTimeout</td>
    042 * <td>{@link Integer}</td>
    043 * <td>Timeout for each neighbour selection (in milliseconds).</td>
    044 * </tr>
    045 * <tr>
    046 * <td>Neighbour.BackTrackDepth</td>
    047 * <td>{@link Integer}</td>
    048 * <td>Limit of search depth.</td>
    049 * </tr>
    050 * </table>
    051 *
    052 * @author  Tomáš Müller
    053 * @version StudentSct 1.3 (Student Sectioning)<br>
    054 *          Copyright (C) 2007 - 2014 Tomáš Müller<br>
    055 *          <a href="mailto:muller@unitime.org">muller@unitime.org</a><br>
    056 *          <a href="http://muller.unitime.org">http://muller.unitime.org</a><br>
    057 * <br>
    058 *          This library is free software; you can redistribute it and/or modify
    059 *          it under the terms of the GNU Lesser General Public License as
    060 *          published by the Free Software Foundation; either version 3 of the
    061 *          License, or (at your option) any later version. <br>
    062 * <br>
    063 *          This library is distributed in the hope that it will be useful, but
    064 *          WITHOUT ANY WARRANTY; without even the implied warranty of
    065 *          MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
    066 *          Lesser General Public License for more details. <br>
    067 * <br>
    068 *          You should have received a copy of the GNU Lesser General Public
    069 *          License along with this library; if not see
    070 *          <a href='http://www.gnu.org/licenses/'>http://www.gnu.org/licenses/</a>.
    071 *
    072 * @param <V> Variable
    073 * @param <T> Value
    074 */
    075public class BacktrackNeighbourSelection<V extends Variable<V, T>, T extends Value<V, T>> extends StandardNeighbourSelection<V, T> {
    076    private ConflictStatistics<V, T> iStat = null;
    077    private static Logger sLog = org.apache.logging.log4j.LogManager.getLogger(BacktrackNeighbourSelection.class);
    078    private int iTimeout = 5000;
    079    private int iDepth = 4;
    080    private int iMaxIters = -1;
    081    protected BacktrackNeighbourSelectionContext iContext;
    082
    083    /**
    084     * Constructor
    085     *
    086     * @param properties
    087     *            configuration
    088     * @throws Exception thrown when initialization fails
    089     */
    090    public BacktrackNeighbourSelection(DataProperties properties) throws Exception {
    091        super(properties);
    092        iTimeout = properties.getPropertyInt("Neighbour.BackTrackTimeout", iTimeout);
    093        iDepth = properties.getPropertyInt("Neighbour.BackTrackDepth", iDepth);
    094        iMaxIters = properties.getPropertyInt("Neighbour.BackTrackMaxIters", iMaxIters);
    095    }
    096
    097    /** Solver initialization */
    098    @Override
    099    public void init(Solver<V, T> solver) {
    100        super.init(solver);
    101        for (Extension<V, T> extension : solver.getExtensions()) {
    102            if (ConflictStatistics.class.isInstance(extension))
    103                iStat = (ConflictStatistics<V, T>) extension;
    104        }
    105    }
    106
    107    /**
    108     * Select neighbour. The standard variable selection (see
    109     * {@link StandardNeighbourSelection#getVariableSelection()}) is used to
    110     * select a variable. A backtracking of a limited depth is than employed
    111     * from this variable. The best assignment found is returned (see
    112     * {@link BackTrackNeighbour}).
    113     **/
    114    @Override
    115    public Neighbour<V, T> selectNeighbour(Solution<V, T> solution) {
    116        return selectNeighbour(solution, getVariableSelection().selectVariable(solution));
    117    }
    118
    119    /**
    120     * Select neighbour -- starts from the provided variable. A backtracking of
    121     * a limited depth is employed from the given variable. The best assignment
    122     * found is returned (see {@link BackTrackNeighbour}).
    123     * @param solution current solution
    124     * @param variable selected variable
    125     * @return a neighbour, null if not found
    126     **/
    127    public Neighbour<V, T> selectNeighbour(Solution<V, T> solution, V variable) {
    128        if (variable == null)
    129            return null;
    130
    131        BacktrackNeighbourSelectionContext context = new BacktrackNeighbourSelectionContext(solution);
    132        selectNeighbour(solution, variable, context);
    133        return context.getBackTrackNeighbour();
    134    }
    135
    136    protected void selectNeighbour(Solution<V, T> solution, V variable, BacktrackNeighbourSelectionContext context) {
    137        iContext = context;
    138        Lock lock = solution.getLock().writeLock();
    139        lock.lock();
    140        try {
    141            if (sLog.isDebugEnabled())
    142                sLog.debug("-- before BT (" + variable.getName() + "): nrAssigned=" + solution.getAssignment().nrAssignedVariables() + ",  value=" + solution.getModel().getTotalValue(solution.getAssignment()));
    143
    144            List<V> variables2resolve = new ArrayList<V>(1);
    145            variables2resolve.add(variable);
    146            backtrack(context, variables2resolve, 0, iDepth);
    147
    148            if (sLog.isDebugEnabled())
    149                sLog.debug("-- after  BT (" + variable.getName() + "): nrAssigned=" + solution.getAssignment().nrAssignedVariables() + ",  value=" + solution.getModel().getTotalValue(solution.getAssignment()));
    150        } finally {
    151            lock.unlock();
    152        }
    153
    154        if (sLog.isDebugEnabled())
    155            sLog.debug("-- selected neighbour: " + context.getBackTrackNeighbour());
    156    }
    157
    158    public BacktrackNeighbourSelectionContext getContext() {
    159        return iContext;
    160    }
    161
    162    private boolean containsConstantValues(Collection<T> values) {
    163        for (T value : values) {
    164            if (value.variable() instanceof ConstantVariable && ((ConstantVariable<?>) value.variable()).isConstant())
    165                return true;
    166        }
    167        return false;
    168    }
    169
    170    /** List of values of the given variable that will be considered
    171     * @param context assignment context
    172     * @param variable given variable
    173     * @return values of the given variable that will be considered
    174     **/
    175    protected Iterator<T> values(BacktrackNeighbourSelectionContext context, V variable) {
    176        return variable.values(context.getAssignment()).iterator();
    177    }
    178
    179    /** Check bound
    180     * @param variables2resolve unassigned variables that are in conflict with the current solution
    181     * @param idx position in variables2resolve
    182     * @param depth current depth
    183     * @param value value to check
    184     * @param conflicts conflicting values
    185     * @return bound (best possible improvement)
    186     **/
    187    protected boolean checkBound(List<V> variables2resolve, int idx, int depth, T value, Set<T> conflicts) {
    188        int nrUnassigned = variables2resolve.size() - idx;
    189        if ((nrUnassigned + conflicts.size() > depth)) {
    190            if (sLog.isDebugEnabled())
    191                sLog.debug("        -- too deap");
    192            return false;
    193        }
    194        if (containsConstantValues(conflicts)) {
    195            if (sLog.isDebugEnabled())
    196                sLog.debug("        -- contains constants values");
    197            return false;
    198        }
    199        boolean containAssigned = false;
    200        for (Iterator<T> i = conflicts.iterator(); !containAssigned && i.hasNext();) {
    201            T conflict = i.next();
    202            int confIdx = variables2resolve.indexOf(conflict.variable());
    203            if (confIdx >= 0 && confIdx <= idx) {
    204                if (sLog.isDebugEnabled())
    205                    sLog.debug("        -- contains resolved variable " + conflict.variable());
    206                containAssigned = true;
    207            }
    208        }
    209        if (containAssigned)
    210            return false;
    211        return true;
    212    }
    213
    214    /** Check whether backtrack can continue
    215     * @param context assignment context
    216     * @param variables2resolve unassigned variables that are in conflict with the current solution
    217     * @param idx position in variables2resolve
    218     * @param depth current depth
    219     * @return true if the search can continue
    220     **/
    221    protected boolean canContinue(BacktrackNeighbourSelectionContext context, List<V> variables2resolve, int idx, int depth) {
    222        if (depth <= 0) {
    223            if (sLog.isDebugEnabled())
    224                sLog.debug("    -- depth reached");
    225            return false;
    226        }
    227        if (context.isTimeoutReached()) {
    228            if (sLog.isDebugEnabled())
    229                sLog.debug("    -- timeout reached");
    230            return false;
    231        }
    232        if (context.isMaxItersReached()) {
    233            if (sLog.isDebugEnabled())
    234                sLog.debug("    -- max number of iterations reached");
    235            return false;
    236        }
    237        return true;
    238    }
    239
    240    protected boolean canContinueEvaluation(BacktrackNeighbourSelectionContext context) {
    241        return !context.isMaxItersReached() && !context.isTimeoutReached();
    242    }
    243
    244    /** Backtracking
    245     * @param context assignment context
    246     * @param variables2resolve unassigned variables that are in conflict with the current solution
    247     * @param idx position in variables2resolve
    248     * @param depth current depth
    249     **/
    250    protected void backtrack(BacktrackNeighbourSelectionContext context, List<V> variables2resolve, int idx, int depth) {
    251        if (sLog.isDebugEnabled())
    252            sLog.debug("  -- bt[" + depth + "]: " + idx + " of " + variables2resolve.size() + " " + variables2resolve);
    253        context.incIteration();
    254        int nrUnassigned = variables2resolve.size() - idx;
    255        if (nrUnassigned == 0) {
    256            context.saveBest(variables2resolve);
    257            return;
    258        }
    259        if (!canContinue(context, variables2resolve, idx, depth))
    260            return;
    261        V variable = variables2resolve.get(idx);
    262        if (sLog.isDebugEnabled())
    263            sLog.debug("    -- variable " + variable);
    264        for (Iterator<T> e = values(context, variable); canContinueEvaluation(context) && e.hasNext();) {
    265            T value = e.next();
    266            T current = context.getAssignment().getValue(variable);
    267            if (value.equals(current))
    268                continue;
    269            if (sLog.isDebugEnabled())
    270                sLog.debug("      -- value " + value);
    271            Set<T> conflicts = context.getModel().conflictValues(context.getAssignment(), value);
    272            if (sLog.isDebugEnabled())
    273                sLog.debug("      -- conflicts " + conflicts);
    274            if (!checkBound(variables2resolve, idx, depth, value, conflicts))
    275                continue;
    276            List<V> newVariables2resolve = new ArrayList<V>(variables2resolve);
    277            for (Iterator<T> i = conflicts.iterator(); i.hasNext();) {
    278                T conflict = i.next();
    279                context.getAssignment().unassign(0, conflict.variable());
    280                if (!newVariables2resolve.contains(conflict.variable()))
    281                    newVariables2resolve.add(conflict.variable());
    282            }
    283            if (current != null)
    284                context.getAssignment().unassign(0, current.variable());
    285            context.getAssignment().assign(0, value);
    286            backtrack(context, newVariables2resolve, idx + 1, depth - 1);
    287            if (current == null)
    288                context.getAssignment().unassign(0, variable);
    289            else
    290                context.getAssignment().assign(0, current);
    291            for (Iterator<T> i = conflicts.iterator(); i.hasNext();) {
    292                T conflict = i.next();
    293                context.getAssignment().assign(0, conflict);
    294            }
    295        }
    296    }
    297
    298    /** Backtracking neighbour */
    299    public class BackTrackNeighbour implements Neighbour<V, T> {
    300        private double iTotalValue = 0;
    301        private double iValue = 0;
    302        private List<T> iDifferentAssignments = null;
    303        private Model<V, T> iModel = null;
    304
    305        /**
    306         * Constructor
    307         *
    308         * @param context assignment context
    309         * @param resolvedVariables
    310         *            variables that has been changed
    311         */
    312        public BackTrackNeighbour(BacktrackNeighbourSelectionContext context, List<V> resolvedVariables) {
    313            iTotalValue = context.getModel().getTotalValue(context.getAssignment());
    314            iDifferentAssignments = new ArrayList<T>();
    315            for (V variable : resolvedVariables) {
    316                T value = variable.getAssignment(context.getAssignment());
    317                iDifferentAssignments.add(value);
    318            }
    319            iValue = iTotalValue - context.iValue;
    320            if (sLog.isDebugEnabled())
    321                iModel = context.getModel();
    322        }
    323
    324        /**
    325         * Constructor
    326         *
    327         * @param context assignment context
    328         * @param resolvedVariables
    329         *            variables that has been changed
    330         */
    331        public BackTrackNeighbour(BacktrackNeighbourSelectionContext context,
    332                @SuppressWarnings("unchecked") V... resolvedVariables) {
    333            iTotalValue = context.getModel().getTotalValue(context.getAssignment());
    334            iDifferentAssignments = new ArrayList<T>();
    335            for (V variable : resolvedVariables) {
    336                T value = variable.getAssignment(context.getAssignment());
    337                iDifferentAssignments.add(value);
    338            }
    339            iValue = iTotalValue - context.iValue;
    340            if (sLog.isDebugEnabled())
    341                iModel = context.getModel();
    342        }
    343
    344        /** Neighbour value (solution total value if the neighbour is applied).
    345         * @return value of the new solution
    346         **/
    347        public double getTotalValue() {
    348            return iTotalValue;
    349        }
    350
    351        /**
    352         * Sum of values of variables from the neighbour that change their
    353         * values
    354         */
    355        @Override
    356        public double value(Assignment<V, T> assignment) {
    357            return iValue;
    358        }
    359
    360        /** Neighbour assignments
    361         * @return list of assignments in this neighbour
    362         **/
    363        public List<T> getAssignments() {
    364            return iDifferentAssignments;
    365        }
    366
    367        /**
    368         * Assign the neighbour
    369         */
    370        @Override
    371        public void assign(Assignment<V, T> assignment, long iteration) {
    372            if (sLog.isDebugEnabled())
    373                sLog.debug("-- before assignment: nrAssigned=" + assignment.nrAssignedVariables() + ",  value=" + iModel.getTotalValue(assignment));
    374            if (sLog.isDebugEnabled())
    375                sLog.debug("  " + this);
    376            int idx = 0;
    377            for (Iterator<T> e = iDifferentAssignments.iterator(); e.hasNext(); idx++) {
    378                T p = e.next();
    379                T o = assignment.getValue(p.variable());
    380                if (o != null) {
    381                    if (idx > 0 && iStat != null)
    382                        iStat.variableUnassigned(iteration, o, iDifferentAssignments.get(0));
    383                    assignment.unassign(iteration, p.variable());
    384                }
    385            }
    386            for (T p : iDifferentAssignments) {
    387                assignment.assign(iteration, p);
    388            }
    389            if (sLog.isDebugEnabled())
    390                sLog.debug("-- after assignment: nrAssigned=" + assignment.nrAssignedVariables() + ",  value=" + iModel.getTotalValue(assignment));
    391        }
    392
    393        /**
    394         * Compare two neighbours
    395         * @param solution current solution
    396         * @return comparison
    397         */
    398        public int compareTo(Solution<V, T> solution) {
    399            return Double.compare(iTotalValue, solution.getModel().getTotalValue(solution.getAssignment()));
    400        }
    401
    402        @Override
    403        public String toString() {
    404            StringBuffer sb = new StringBuffer("BT{value=" + iTotalValue + ": ");
    405            for (Iterator<T> e = iDifferentAssignments.iterator(); e.hasNext();) {
    406                T p = e.next();
    407                sb.append("\n    " + p.variable().getName() + " " + p.getName() + (e.hasNext() ? "," : ""));
    408            }
    409            sb.append("}");
    410            return sb.toString();
    411        }
    412
    413        @Override
    414        public Map<V, T> assignments() {
    415            Map<V, T> ret = new HashMap<V, T>();
    416            for (T p : iDifferentAssignments)
    417                ret.put(p.variable(), p);
    418            return ret;
    419        }
    420    }
    421
    422    /** Return maximal depth
    423     * @return maximal search depth
    424     **/
    425    public int getDepth() {
    426        return iDepth;
    427    }
    428
    429    /** Set maximal depth
    430     * @param depth maximal search depth
    431     **/
    432    public void setDepth(int depth) {
    433        iDepth = depth;
    434    }
    435
    436    /** Return time limit
    437     * @return time limit
    438     **/
    439    public int getTimeout() {
    440        return iTimeout;
    441    }
    442
    443    /** Set time limit
    444     * @param timeout time limit
    445     **/
    446    public void setTimeout(int timeout) {
    447        iTimeout = timeout;
    448    }
    449
    450    /** Return maximal number of iterations
    451     * @return maximal number of iterations
    452     **/
    453    public int getMaxIters() {
    454        return iMaxIters;
    455    }
    456
    457    /** Set maximal number of iterations
    458     * @param maxIters maximal number of iterations
    459     **/
    460    public void setMaxIters(int maxIters) {
    461        iMaxIters = maxIters;
    462    }
    463
    464    public class BacktrackNeighbourSelectionContext implements AssignmentContext {
    465        private long iT0, iT1 = 0;
    466        private boolean iTimeoutReached = false;
    467        private int iMaxIters = -1, iNrIters = 0;
    468        protected Solution<V, T> iSolution = null;
    469        protected BackTrackNeighbour iBackTrackNeighbour = null;
    470        protected double iValue = 0;
    471        private int iNrAssigned = 0;
    472        private boolean iMaxItersReached = false;
    473
    474        public BacktrackNeighbourSelectionContext(Solution<V, T> solution) {
    475            iSolution = solution;
    476            iBackTrackNeighbour = null;
    477            iValue = solution.getModel().getTotalValue(iSolution.getAssignment());
    478            iNrAssigned = iSolution.getAssignment().nrAssignedVariables();
    479            iT0 = JProf.currentTimeMillis();
    480            iNrIters = 0;
    481            iTimeoutReached = false;
    482            iMaxItersReached = false;
    483        }
    484
    485        /** Time needed to find a neighbour (last call of selectNeighbour method)
    486         * @return search time
    487         **/
    488        public long getTime() {
    489            if (iT1 == 0) return JProf.currentTimeMillis() - iT0;
    490            return iT1 - iT0;
    491        }
    492
    493        /**
    494         * True, if timeout was reached during the last call of selectNeighbour
    495         * method
    496         * @return true if the timeout was reached
    497         */
    498        public boolean isTimeoutReached() {
    499            return iTimeoutReached;
    500        }
    501
    502        /**
    503         * True, if the maximum number of iterations was reached by the last call of
    504         * selectNeighbour method
    505         * @return true if the maximum number of iterations was reached
    506         */
    507        public boolean isMaxItersReached() {
    508            return iMaxItersReached;
    509        }
    510
    511        public BackTrackNeighbour getBackTrackNeighbour() { return iBackTrackNeighbour; }
    512
    513        public void incIteration() {
    514            iT1 = JProf.currentTimeMillis();
    515            if (!iTimeoutReached && iTimeout > 0 && iT1 - iT0 > iTimeout)
    516                iTimeoutReached = true;
    517            if (!iMaxItersReached && iMaxIters > 0 && iNrIters++ > iMaxIters)
    518                iMaxItersReached = true;
    519        }
    520
    521        public void saveBest(List<V> variables2resolve) {
    522            if (sLog.isDebugEnabled())
    523                sLog.debug("    -- all assigned");
    524            if (iSolution.getAssignment().nrAssignedVariables() > iNrAssigned || (iSolution.getAssignment().nrAssignedVariables() == iNrAssigned && iValue > iSolution.getModel().getTotalValue(iSolution.getAssignment()))) {
    525                if (sLog.isDebugEnabled())
    526                    sLog.debug("    -- better than current");
    527                if (iBackTrackNeighbour == null || iBackTrackNeighbour.compareTo(iSolution) >= 0) {
    528                    if (sLog.isDebugEnabled())
    529                        sLog.debug("      -- better than best");
    530                    iBackTrackNeighbour = new BackTrackNeighbour(this, variables2resolve);
    531                }
    532            }
    533        }
    534
    535        public void saveBest(@SuppressWarnings("unchecked") V... variables2resolve) {
    536            if (sLog.isDebugEnabled())
    537                sLog.debug("    -- all assigned");
    538            if (iSolution.getAssignment().nrAssignedVariables() > iNrAssigned || (iSolution.getAssignment().nrAssignedVariables() == iNrAssigned && iValue > iSolution.getModel().getTotalValue(iSolution.getAssignment()))) {
    539                if (sLog.isDebugEnabled())
    540                    sLog.debug("    -- better than current");
    541                if (iBackTrackNeighbour == null || iBackTrackNeighbour.compareTo(iSolution) >= 0) {
    542                    if (sLog.isDebugEnabled())
    543                        sLog.debug("      -- better than best");
    544                    iBackTrackNeighbour = new BackTrackNeighbour(this, variables2resolve);
    545                }
    546            }
    547        }
    548
    549        public Model<V, T> getModel() { return iSolution.getModel();}
    550
    551        public Assignment<V, T> getAssignment() { return iSolution.getAssignment(); }
    552    }
    553}