    001package net.sf.cpsolver.ifs.heuristics;
    002
    003import java.util.ArrayList;
    004import java.util.Collection;
    005import java.util.Iterator;
    006import java.util.List;
    007import java.util.Set;
    008
    009import net.sf.cpsolver.ifs.constant.ConstantVariable;
    010import net.sf.cpsolver.ifs.extension.ConflictStatistics;
    011import net.sf.cpsolver.ifs.extension.Extension;
    012import net.sf.cpsolver.ifs.model.Neighbour;
    013import net.sf.cpsolver.ifs.model.Value;
    014import net.sf.cpsolver.ifs.model.Variable;
    015import net.sf.cpsolver.ifs.solution.Solution;
    016import net.sf.cpsolver.ifs.solver.Solver;
    017import net.sf.cpsolver.ifs.util.DataProperties;
    018import net.sf.cpsolver.ifs.util.JProf;
    019
    020import org.apache.log4j.Logger;
    021
    022/**
    023 * Backtracking-based neighbour selection. A best neighbour that is found by a
    024 * backtracking-based algorithm within a limited depth from a selected variable
    025 * is returned. <br>
    026 * <br>
    027 * Parameters: <br>
    028 * <table border='1'>
    029 * <tr>
    030 * <th>Parameter</th>
    031 * <th>Type</th>
    032 * <th>Comment</th>
    033 * </tr>
    034 * <tr>
    035 * <td>Neighbour.BackTrackTimeout</td>
    036 * <td>{@link Integer}</td>
    037 * <td>Timeout for each neighbour selection (in milliseconds).</td>
    038 * </tr>
    039 * <tr>
    040 * <td>Neighbour.BackTrackDepth</td>
    041 * <td>{@link Integer}</td>
    042 * <td>Limit of search depth.</td>
    043 * </tr>
    044 * </table>
    045 *
    046 * <br>
    047 * <br>
    048 *
    049 * @version StudentSct 1.2 (Student Sectioning)<br>
    050 *          Copyright (C) 2007 - 2010 Tomáš Müller<br>
    051 *          <a href="mailto:muller@unitime.org">muller@unitime.org</a><br>
    052 *          <a href="http://muller.unitime.org">http://muller.unitime.org</a><br>
    053 * <br>
    054 *          This library is free software; you can redistribute it and/or modify
    055 *          it under the terms of the GNU Lesser General Public License as
    056 *          published by the Free Software Foundation; either version 3 of the
    057 *          License, or (at your option) any later version. <br>
    058 * <br>
    059 *          This library is distributed in the hope that it will be useful, but
    060 *          WITHOUT ANY WARRANTY; without even the implied warranty of
    061 *          MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
    062 *          Lesser General Public License for more details. <br>
    063 * <br>
    064 *          You should have received a copy of the GNU Lesser General Public
    065 *          License along with this library; if not see
    066 *          <a href='http://www.gnu.org/licenses/'>http://www.gnu.org/licenses/</a>.
    067 */
    068
    069public class BacktrackNeighbourSelection<V extends Variable<V, T>, T extends Value<V, T>> extends
    070        StandardNeighbourSelection<V, T> {
    071    private ConflictStatistics<V, T> iStat = null;
    072    private static Logger sLog = Logger.getLogger(BacktrackNeighbourSelection.class);
    073    private int iTimeout = 5000;
    074    private int iDepth = 4;
    075
    076    protected Solution<V, T> iSolution = null;
    077    protected BackTrackNeighbour iBackTrackNeighbour = null;
    078    protected double iValue = 0;
    079    private int iNrAssigned = 0;
    080    private long iT0, iT1;
    081    private boolean iTimeoutReached = false;
    082    private int iMaxIters = -1, iNrIters = 0;
    083    private boolean iMaxItersReached = false;
    084
    085    /**
    086     * Constructor
    087     *
    088     * @param properties
    089     *            configuration
    090     * @throws Exception
    091     */
    092    public BacktrackNeighbourSelection(DataProperties properties) throws Exception {
    093        super(properties);
    094        iTimeout = properties.getPropertyInt("Neighbour.BackTrackTimeout", iTimeout);
    095        iDepth = properties.getPropertyInt("Neighbour.BackTrackDepth", iDepth);
    096        iMaxIters = properties.getPropertyInt("Neighbour.BackTrackMaxIters", iMaxIters);
    097    }
    098
    099    /** Solver initialization */
    100    @Override
    101    public void init(Solver<V, T> solver) {
    102        super.init(solver);
    103        for (Extension<V, T> extension : solver.getExtensions()) {
    104            if (ConflictStatistics.class.isInstance(extension))
    105                iStat = (ConflictStatistics<V, T>) extension;
    106        }
    107    }
    108
    109    /**
    110     * Select neighbour. The standard variable selection (see
    111     * {@link StandardNeighbourSelection#getVariableSelection()}) is used to
    112     * select a variable. A backtracking of a limited depth is than employed
    113     * from this variable. The best assignment found is returned (see
    114     * {@link BackTrackNeighbour}).
    115     **/
    116    @Override
    117    public Neighbour<V, T> selectNeighbour(Solution<V, T> solution) {
    118        return selectNeighbour(solution, getVariableSelection().selectVariable(solution));
    119    }
    120
    121    /**
    122     * Select neighbour -- starts from the provided variable. A backtracking of
    123     * a limited depth is employed from the given variable. The best assignment
    124     * found is returned (see {@link BackTrackNeighbour}).
    125     **/
    126    public synchronized Neighbour<V, T> selectNeighbour(Solution<V, T> solution, V variable) {
    127        if (variable == null)
    128            return null;
    129
    130        iSolution = solution;
    131        iBackTrackNeighbour = null;
    132        iValue = solution.getModel().getTotalValue();
    133        iNrAssigned = solution.getModel().assignedVariables().size();
    134        iT0 = JProf.currentTimeMillis();
    135        iNrIters = 0;
    136        iTimeoutReached = false;
    137        iMaxItersReached = false;
    138
    139        synchronized (solution) {
    140            if (sLog.isDebugEnabled())
    141                sLog.debug("-- before BT (" + variable.getName() + "): nrAssigned="
    142                        + iSolution.getModel().assignedVariables().size() + ",  value="
    143                        + iSolution.getModel().getTotalValue());
    144
    145            List<V> variables2resolve = new ArrayList<V>(1);
    146            variables2resolve.add(variable);
    147            backtrack(variables2resolve, 0, iDepth);
    148
    149            if (sLog.isDebugEnabled())
    150                sLog.debug("-- after  BT (" + variable.getName() + "): nrAssigned="
    151                        + iSolution.getModel().assignedVariables().size() + ",  value="
    152                        + iSolution.getModel().getTotalValue());
    153        }
    154
    155        iT1 = JProf.currentTimeMillis();
    156
    157        if (sLog.isDebugEnabled())
    158            sLog.debug("-- selected neighbour: " + iBackTrackNeighbour);
    159        return iBackTrackNeighbour;
    160    }
    161
    162    /** Time needed to find a neighbour (last call of selectNeighbour method) */
    163    public long getTime() {
    164        return iT1 - iT0;
    165    }
    166
    167    /**
    168     * True, if timeout was reached during the last call of selectNeighbour
    169     * method
    170     */
    171    public boolean isTimeoutReached() {
    172        return iTimeoutReached;
    173    }
    174
    175    /**
    176     * True, if the maximum number of iterations was reached by the last call of
    177     * selectNeighbour method
    178     */
    179    public boolean isMaxItersReached() {
    180        return iMaxItersReached;
    181    }
    182
    183    private boolean containsConstantValues(Collection<T> values) {
    184        for (T value : values) {
    185            if (value.variable() instanceof ConstantVariable && ((ConstantVariable) value.variable()).isConstant())
    186                return true;
    187        }
    188        return false;
    189    }
    190
    191    /** List of values of the given variable that will be considered */
    192    protected Iterator<T> values(V variable) {
    193        return variable.values().iterator();
    194    }
    195
    196    /** Check bound */
    197    protected boolean checkBound(List<V> variables2resolve, int idx, int depth, T value, Set<T> conflicts) {
    198        int nrUnassigned = variables2resolve.size() - idx;
    199        if ((nrUnassigned + conflicts.size() > depth)) {
    200            if (sLog.isDebugEnabled())
    201                sLog.debug("        -- too deap");
    202            return false;
    203        }
    204        if (containsConstantValues(conflicts)) {
    205            if (sLog.isDebugEnabled())
    206                sLog.debug("        -- contains constants values");
    207            return false;
    208        }
    209        boolean containAssigned = false;
    210        for (Iterator<T> i = conflicts.iterator(); !containAssigned && i.hasNext();) {
    211            T conflict = i.next();
    212            int confIdx = variables2resolve.indexOf(conflict.variable());
    213            if (confIdx >= 0 && confIdx <= idx) {
    214                if (sLog.isDebugEnabled())
    215                    sLog.debug("        -- contains resolved variable " + conflict.variable());
    216                containAssigned = true;
    217            }
    218        }
    219        if (containAssigned)
    220            return false;
    221        return true;
    222    }
    223
    224    /** Check whether backtrack can continue */
    225    protected boolean canContinue(List<V> variables2resolve, int idx, int depth) {
    226        if (depth <= 0) {
    227            if (sLog.isDebugEnabled())
    228                sLog.debug("    -- depth reached");
    229            return false;
    230        }
    231        if (iTimeoutReached) {
    232            if (sLog.isDebugEnabled())
    233                sLog.debug("    -- timeout reached");
    234            return false;
    235        }
    236        if (iMaxItersReached) {
    237            if (sLog.isDebugEnabled())
    238                sLog.debug("    -- max number of iterations reached");
    239            return false;
    240        }
    241        return true;
    242    }
    243
    244    protected boolean canContinueEvaluation() {
    245        return !iTimeoutReached && !iMaxItersReached;
    246    }
    247
    248    /** Backtracking */
    249    protected void backtrack(List<V> variables2resolve, int idx, int depth) {
    250        if (sLog.isDebugEnabled())
    251            sLog.debug("  -- bt[" + depth + "]: " + idx + " of " + variables2resolve.size() + " " + variables2resolve);
    252        if (!iTimeoutReached && iTimeout > 0 && JProf.currentTimeMillis() - iT0 > iTimeout)
    253            iTimeoutReached = true;
    254        if (!iMaxItersReached && iMaxIters > 0 && iNrIters++ > iMaxIters)
    255            iMaxItersReached = true;
    256        int nrUnassigned = variables2resolve.size() - idx;
    257        if (nrUnassigned == 0) {
    258            if (sLog.isDebugEnabled())
    259                sLog.debug("    -- all assigned");
    260            if (iSolution.getModel().assignedVariables().size() > iNrAssigned
    261                    || (iSolution.getModel().assignedVariables().size() == iNrAssigned && iValue > iSolution.getModel()
    262                            .getTotalValue())) {
    263                if (sLog.isDebugEnabled())
    264                    sLog.debug("    -- better than current");
    265                if (iBackTrackNeighbour == null || iBackTrackNeighbour.compareTo(iSolution) >= 0) {
    266                    if (sLog.isDebugEnabled())
    267                        sLog.debug("      -- better than best");
    268                    iBackTrackNeighbour = new BackTrackNeighbour(variables2resolve);
    269                }
    270            }
    271            return;
    272        }
    273        if (!canContinue(variables2resolve, idx, depth))
    274            return;
    275        V variable = variables2resolve.get(idx);
    276        if (sLog.isDebugEnabled())
    277            sLog.debug("    -- variable " + variable);
    278        for (Iterator<T> e = values(variable); canContinueEvaluation() && e.hasNext();) {
    279            T value = e.next();
    280            if (value.equals(variable.getAssignment()))
    281                continue;
    282            if (sLog.isDebugEnabled())
    283                sLog.debug("      -- value " + value);
    284            Set<T> conflicts = iSolution.getModel().conflictValues(value);
    285            if (sLog.isDebugEnabled())
    286                sLog.debug("      -- conflicts " + conflicts);
    287            if (!checkBound(variables2resolve, idx, depth, value, conflicts))
    288                continue;
    289            T current = variable.getAssignment();
    290            List<V> newVariables2resolve = new ArrayList<V>(variables2resolve);
    291            for (Iterator<T> i = conflicts.iterator(); i.hasNext();) {
    292                T conflict = i.next();
    293                conflict.variable().unassign(0);
    294                if (!newVariables2resolve.contains(conflict.variable()))
    295                    newVariables2resolve.add(conflict.variable());
    296            }
    297            if (current != null)
    298                current.variable().unassign(0);
    299            value.variable().assign(0, value);
    300            backtrack(newVariables2resolve, idx + 1, depth - 1);
    301            if (current == null)
    302                variable.unassign(0);
    303            else
    304                variable.assign(0, current);
    305            for (Iterator<T> i = conflicts.iterator(); i.hasNext();) {
    306                T conflict = i.next();
    307                conflict.variable().assign(0, conflict);
    308            }
    309        }
    310    }
    311
    312    /** Backtracking neighbour */
    313    public class BackTrackNeighbour extends Neighbour<V, T> {
    314        private double iTotalValue = 0;
    315        private double iValue = 0;
    316        private List<T> iDifferentAssignments = null;
    317
    318        /**
    319         * Constructor
    320         *
    321         * @param resolvedVariables
    322         *            variables that has been changed
    323         */
    324        public BackTrackNeighbour(List<V> resolvedVariables) {
    325            iTotalValue = iSolution.getModel().getTotalValue();
    326            iValue = 0;
    327            iDifferentAssignments = new ArrayList<T>();
    328            for (V variable : resolvedVariables) {
    329                T value = variable.getAssignment();
    330                iDifferentAssignments.add(value);
    331                iValue += value.toDouble();
    332            }
    333        }
    334
    335        /** Neighbour value (solution total value if the neighbour is applied). */
    336        public double getTotalValue() {
    337            return iTotalValue;
    338        }
    339
    340        /**
    341         * Sum of values of variables from the neighbour that change their
    342         * values
    343         */
    344        @Override
    345        public double value() {
    346            return iValue;
    347        }
    348
    349        /** Neighbour assignments */
    350        public List<T> getAssignments() {
    351            return iDifferentAssignments;
    352        }
    353
    354        /**
    355         * Assign the neighbour
    356         */
    357        @Override
    358        public void assign(long iteration) {
    359            if (sLog.isDebugEnabled())
    360                sLog.debug("-- before assignment: nrAssigned=" + iSolution.getModel().assignedVariables().size()
    361                        + ",  value=" + iSolution.getModel().getTotalValue());
    362            if (sLog.isDebugEnabled())
    363                sLog.debug("  " + this);
    364            int idx = 0;
    365            for (Iterator<T> e = iDifferentAssignments.iterator(); e.hasNext(); idx++) {
    366                T p = e.next();
    367                if (p.variable().getAssignment() != null) {
    368                    if (idx > 0 && iStat != null)
    369                        iStat.variableUnassigned(iteration, p.variable().getAssignment(), iDifferentAssignments.get(0));
    370                    p.variable().unassign(iteration);
    371                }
    372            }
    373            for (T p : iDifferentAssignments) {
    374                p.variable().assign(iteration, p);
    375            }
    376            if (sLog.isDebugEnabled())
    377                sLog.debug("-- after assignment: nrAssigned=" + iSolution.getModel().assignedVariables().size()
    378                        + ",  value=" + iSolution.getModel().getTotalValue());
    379        }
    380
    381        /**
    382         * Compare two neighbours
    383         */
    384        public int compareTo(Solution<V, T> solution) {
    385            return Double.compare(iTotalValue, solution.getModel().getTotalValue());
    386        }
    387
    388        @Override
    389        public String toString() {
    390            StringBuffer sb = new StringBuffer("BT{value=" + (iTotalValue - iSolution.getModel().getTotalValue())
    391                    + ": ");
    392            for (Iterator<T> e = iDifferentAssignments.iterator(); e.hasNext();) {
    393                T p = e.next();
    394                sb.append("\n    " + p.variable().getName() + " " + p.getName() + (e.hasNext() ? "," : ""));
    395            }
    396            sb.append("}");
    397            return sb.toString();
    398        }
    399    }
    400
    401    /** Return maximal depth */
    402    public int getDepth() {
    403        return iDepth;
    404    }
    405
    406    /** Set maximal depth */
    407    public void setDepth(int depth) {
    408        iDepth = depth;
    409    }
    410
    411    /** Return time limit */
    412    public int getTimeout() {
    413        return iTimeout;
    414    }
    415
    416    /** Set time limit */
    417    public void setTimeout(int timeout) {
    418        iTimeout = timeout;
    419    }
    420
    421    /** Return maximal number of iterations */
    422    public int getMaxIters() {
    423        return iMaxIters;
    424    }
    425
    426    /** Set maximal number of iterations */
    427    public void setMaxIters(int maxIters) {
    428        iMaxIters = maxIters;
    429    }
    430}