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