    001package org.cpsolver.ifs.extension;
    002
    003import java.util.ArrayList;
    004import java.util.Collection;
    005import java.util.Comparator;
    006import java.util.HashMap;
    007import java.util.List;
    008import java.util.Map;
    009import java.util.Set;
    010import java.util.TreeSet;
    011import java.util.concurrent.locks.ReentrantReadWriteLock;
    012
    013import org.cpsolver.ifs.assignment.Assignment;
    014import org.cpsolver.ifs.heuristics.ValueSelection;
    015import org.cpsolver.ifs.heuristics.VariableSelection;
    016import org.cpsolver.ifs.model.Constraint;
    017import org.cpsolver.ifs.model.ConstraintListener;
    018import org.cpsolver.ifs.model.Model;
    019import org.cpsolver.ifs.model.Value;
    020import org.cpsolver.ifs.model.Variable;
    021import org.cpsolver.ifs.solution.Solution;
    022import org.cpsolver.ifs.solver.Solver;
    023import org.cpsolver.ifs.util.DataProperties;
    024
    025
    026/**
    027 * Conflict-based statistics. <br>
    028 * <br>
    029 * The idea behind it is to memorize conflicts and to avoid their potential
    030 * repetition. When a value v0 is assigned to a variable V0, hard conflicts with
    031 * previously assigned variables (e.g., V1 = v1, V2 = v2, ... Vm = vm) may
    032 * occur. These variables V1,...,Vm have to be unassigned before the value v0 is
    033 * assigned to the variable V0. These unassignments, together with the reason
    034 * for their unassignment (i.e., the assignment V0 = v0), and a counter tracking
    035 * how many times such an event occurred in the past, is stored in memory. <br>
    036 * <br>
    037 * Later, if a variable is selected for assignment again, the stored information
    038 * about repetition of past hard conflicts can be taken into account, e.g., in
    039 * the value selection heuristics. Assume that the variable V0 is selected for
    040 * an assignment again (e.g., because it became unassigned as a result of a
    041 * later assignment), we can weight the number of hard conflicts created in the
    042 * past for each possible value of this variable. In the above example, the
    043 * existing assignment V1 = v1 can prohibit the selection of value v0 for
    044 * variable V0 if there is again a conflict with the assignment V1 = v1. <br>
    045 * <br>
    046 * Conflict-based statistics are a data structure which memorizes the number of
    047 * hard conflicts that have occurred during the search (e.g., that assignment V0
    048 * = v0 resulted c1 times in an unassignment of V1 = v1, c2 times of V2 = v2, .
    049 * . . and cm times of Vm = vm). More precisely, they form an array
    050 * <pre><code>
    051 * CBS[Va = va, Vb != vb] = cab,
    052 * </code></pre>
    053 * stating that the assignment Va = va caused the unassignment of Vb = vb a
    054 * total of cab times in the past. Note that in case of n-ary constraints (where
    055 * n &gt; 2), this does not imply that the assignments Va = va and Vb = vb cannot
    056 * be used together. The proposed conflict-based statistics do not actually work
    057 * with any constraint, they only memorize unassignments and the assignment that
    058 * caused them. Let us consider a variable Va selected by the
    059 * {@link VariableSelection#selectVariable(Solution)} function and a value va
    060 * selected by {@link ValueSelection#selectValue(Solution, Variable)}. Once the
    061 * assignment Vb = vb is selected by {@link Model#conflictValues(Assignment, Value)} to be
    062 * unassigned, the array cell CBS[Va = va, Vb != vb] is incremented by one. <br>
    063 * <br>
    064 * The data structure is implemented as a hash table, storing information for
    065 * conflict-based statistics. A counter is maintained for the tuple A = a and B
    066 * != b. This counter is increased when the value a is assigned to the variable
    067 * A and b is unassigned from B. The example of this structure
    068 * <pre><code>
    069 * A = a &nbsp;&nbsp;&nbsp; &#8594; &nbsp;&nbsp;&nbsp; 3 x B != b, &nbsp; 4 x B
    070 * != c, &nbsp; 2 x C != a, &nbsp; 120 x D != a
    071 * </code></pre>
    072 * expresses that variable B lost its assignment b three times and its
    073 * assignment c four times, variable C lost its assignment a two times, and D
    074 * lost its assignment a 120 times, all because of later assignments of value a
    075 * to variable A. This structure is being used in the value selection heuristics
    076 * to evaluate existing conflicts with the assigned variables. For example, if
    077 * there is a variable A selected and if the value a is in conflict with the
    078 * assignment B = b, we know that a similar problem has already occurred 3x in
    079 * the past, and hence the conflict A = a is weighted with the number 3. <br>
    080 * <br>
    081 * Then, a min-conflict value selection criterion, which selects a value with
    082 * the minimal number of conflicts with the existing assignments, can be easily
    083 * adapted to a weighted min-conflict criterion. The value with the smallest sum
    084 * of the number of conflicts multiplied by their frequencies is selected.
    085 * Stated in another way, the weighted min-conflict approach helps the value
    086 * selection heuristics to select a value that might cause more conflicts than
    087 * another value, but these conflicts occurred less frequently, and therefore
    088 * they have a lower weighted sum. <br>
    089 * <br>
    090 * The conflict-based statistics has also implemented the following extensions:
    091 * <ul>
    092 * <li>If a variable is selected for an assignment, the above presented
    093 * structure can also tell how many potential conflicts a value can cause in the
    094 * future. In the above example, we already know that four times a later
    095 * assignment of A=a caused that value c was unassigned from B. We can try to
    096 * minimize such future conflicts by selecting a different value of the variable
    097 * B while A is still unbound.
    098 * <li>The memorized conflicts can be aged according to how far they have
    099 * occurred in the past. For example, a conflict which occurred 1000 iterations
    100 * ago can have half the weight of a conflict which occurred during the last
    101 * iteration or it can be forgotten at all.
    102 * </ul>
    103 * Furthermore, the presented conflict-based statistics can be used not only
    104 * inside the solving mechanism. The constructed "implications" together with
    105 * the information about frequency of their occurrences can be easily accessed
    106 * by users or by some add-on deductive engine to identify inconsistencies1
    107 * and/or hard parts of the input problem. The user can then modify the input
    108 * requirements in order to eliminate problems found and let the solver continue
    109 * the search with this modified input problem. <br>
    110 * <br>
    111 * Parameters: <br>
    112 * <table border='1' summary='Related Solver Parameters'>
    113 * <tr>
    114 * <th>Parameter</th>
    115 * <th>Type</th>
    116 * <th>Comment</th>
    117 * </tr>
    118 * <tr>
    119 * <td>ConflictStatistics.Ageing</td>
    120 * <td>{@link Double}</td>
    121 * <td>Ageing of the conflict-based statistics. Every memorized conflict is aged
    122 * (multiplited) by this factor for every iteration which passed from the time
    123 * it was memorized. For instance, if there was a conflict 10 iterations ago,
    124 * its value is ageing^10 (default is 1.0 -- no ageing).</td>
    125 * </tr>
    126 * <tr>
    127 * <td>ConflictStatistics.AgeingHalfTime</td>
    128 * <td>{@link Integer}</td>
    129 * <td>Another way how to express ageing: number of iterations to decrease a
    130 * conflict to 1/2 (default is 0 -- no ageing)</td>
    131 * </tr>
    132 * </table>
    133 *
    134 * @see Solver
    135 * @see Model
    136 * @see ValueSelection
    137 * @see VariableSelection
    138 *
    139 * @version IFS 1.3 (Iterative Forward Search)<br>
    140 *          Copyright (C) 2006 - 2014 Tomáš Müller<br>
    141 *          <a href="mailto:muller@unitime.org">muller@unitime.org</a><br>
    142 *          <a href="http://muller.unitime.org">http://muller.unitime.org</a><br>
    143 * <br>
    144 *          This library is free software; you can redistribute it and/or modify
    145 *          it under the terms of the GNU Lesser General Public License as
    146 *          published by the Free Software Foundation; either version 3 of the
    147 *          License, or (at your option) any later version. <br>
    148 * <br>
    149 *          This library is distributed in the hope that it will be useful, but
    150 *          WITHOUT ANY WARRANTY; without even the implied warranty of
    151 *          MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
    152 *          Lesser General Public License for more details. <br>
    153 * <br>
    154 *          You should have received a copy of the GNU Lesser General Public
    155 *          License along with this library; if not see
    156 *          <a href='http://www.gnu.org/licenses/'>http://www.gnu.org/licenses/</a>.
    157 * @param <V> Variable
    158 * @param <T> Value
    159 */
    160public class ConflictStatistics<V extends Variable<V, T>, T extends Value<V, T>> extends Extension<V, T> implements ConstraintListener<V, T> {
    161    private static final String PARAM_AGEING = "ConflictStatistics.Ageing";
    162    private static final String PARAM_HALF_AGE = "ConflictStatistics.AgeingHalfTime";
    163    private static final String PARAM_PRINT = "ConflictStatistics.Print";
    164
    165    private double iAgeing = 1.0;
    166    private boolean iPrint = false;
    167
    168    private Map<AssignedValue<T>, List<AssignedValue<T>>> iAssignments = new HashMap<AssignedValue<T>, List<AssignedValue<T>>>();
    169    private Map<V, List<AssignedValue<T>>> iUnassignedVariables = new HashMap<V, List<AssignedValue<T>>>();
    170    private Map<AssignedValue<T>, List<AssignedValue<T>>> iNoGoods = new HashMap<AssignedValue<T>, List<AssignedValue<T>>>();
    171
    172    private final ReentrantReadWriteLock iLock = new ReentrantReadWriteLock();
    173
    174    public ConflictStatistics(Solver<V, T> solver, DataProperties properties) {
    175        super(solver, properties);
    176        iAgeing = properties.getPropertyDouble(PARAM_AGEING, iAgeing);
    177        int halfAge = properties.getPropertyInt(PARAM_HALF_AGE, 0);
    178        if (halfAge > 0)
    179            iAgeing = Math.exp(Math.log(0.5) / (halfAge));
    180        iPrint = properties.getPropertyBoolean(PARAM_PRINT, iPrint);
    181    }
    182
    183    @Override
    184    public void register(Model<V, T> model) {
    185        super.register(model);
    186    }
    187
    188    @Override
    189    public void unregister(Model<V, T> model) {
    190        super.unregister(model);
    191    }
    192
    193    private void variableUnassigned(long iteration, T unassignedValue, AssignedValue<T> noGood) {
    194        if (iteration <= 0) return;
    195        iLock.writeLock().lock();
    196        try {
    197            AssignedValue<T> unass = new AssignedValue<T>(iteration, unassignedValue, iAgeing);
    198            List<AssignedValue<T>> noGoodsForUnassignment = iNoGoods.get(unass);
    199            if (noGoodsForUnassignment != null) {
    200                if (noGoodsForUnassignment.contains(noGood)) {
    201                    (noGoodsForUnassignment.get(noGoodsForUnassignment.indexOf(noGood))).incCounter(iteration);
    202                } else {
    203                    noGoodsForUnassignment.add(noGood);
    204                }
    205            } else {
    206                noGoodsForUnassignment = new ArrayList<AssignedValue<T>>();
    207                noGoodsForUnassignment.add(noGood);
    208                iNoGoods.put(unass, noGoodsForUnassignment);
    209            }
    210        } finally {
    211            iLock.writeLock().unlock();
    212        }
    213    }
    214
    215    public void reset() {
    216        iLock.writeLock().lock();
    217        try {
    218            iUnassignedVariables.clear();
    219            iAssignments.clear();
    220        } finally {
    221            iLock.writeLock().unlock();
    222        }
    223    }
    224
    225    public Map<AssignedValue<T>, List<AssignedValue<T>>> getNoGoods() {
    226        return iNoGoods;
    227    }
    228
    229    public void variableUnassigned(long iteration, T unassignedValue, T assignedValue) {
    230        if (iteration <= 0) return;
    231        AssignedValue<T> ass = new AssignedValue<T>(iteration, assignedValue, iAgeing);
    232        AssignedValue<T> unass = new AssignedValue<T>(iteration, unassignedValue, iAgeing);
    233        iLock.writeLock().lock();
    234        try {
    235            if (iAssignments.containsKey(unass)) {
    236                List<AssignedValue<T>> asss = iAssignments.get(unass);
    237                if (asss.contains(ass)) {
    238                    asss.get(asss.indexOf(ass)).incCounter(iteration);
    239                } else {
    240                    asss.add(ass);
    241                }
    242            } else {
    243                List<AssignedValue<T>> asss = new ArrayList<AssignedValue<T>>();
    244                asss.add(ass);
    245                iAssignments.put(unass, asss);
    246            }
    247            if (iUnassignedVariables.containsKey(unassignedValue.variable())) {
    248                List<AssignedValue<T>> asss = iUnassignedVariables.get(unassignedValue.variable());
    249                if (asss.contains(ass)) {
    250                    (asss.get(asss.indexOf(ass))).incCounter(iteration);
    251                } else {
    252                    asss.add(ass);
    253                }
    254            } else {
    255                List<AssignedValue<T>> asss = new ArrayList<AssignedValue<T>>();
    256                asss.add(ass);
    257                iUnassignedVariables.put(unassignedValue.variable(), asss);
    258            }
    259        } finally {
    260            iLock.writeLock().unlock();
    261        }
    262    }
    263
    264    /**
    265     * Counts number of unassignments of the given conflicting values caused by
    266     * the assignment of the given value.
    267     * @param iteration current iteration
    268     * @param conflictValues values conflicting with the given value
    269     * @param value given value
    270     * @return number of unassignments
    271     */
    272    public double countRemovals(long iteration, Collection<T> conflictValues, T value) {
    273        long ret = 0;
    274        for (T conflictValue : conflictValues) {
    275            ret += countRemovals(iteration, conflictValue, value);
    276            // tady bylo +1
    277        }
    278        return ret;
    279    }
    280
    281    /**
    282     * Counts number of unassignments of the given conflicting value caused by
    283     * the assignment of the given value.
    284     * @param iteration current iteration
    285     * @param conflictValue value conflicting with the given value
    286     * @param value given value
    287     * @return number of unassignments
    288     */
    289    public double countRemovals(long iteration, T conflictValue, T value) {
    290        iLock.readLock().lock();
    291        try {
    292            List<AssignedValue<T>> asss = iUnassignedVariables.get(conflictValue.variable());
    293            if (asss == null)
    294                return 0;
    295            AssignedValue<T> ass = new AssignedValue<T>(iteration, value, iAgeing);
    296            int idx = asss.indexOf(ass);
    297            if (idx < 0)
    298                return 0;
    299            return (asss.get(idx)).getCounter(iteration);
    300        } finally {
    301            iLock.readLock().unlock();
    302        }
    303    }
    304
    305    /**
    306     * Counts potential number of unassignments of if the given value is
    307     * selected.
    308     * @param assignment current assignment
    309     * @param iteration current iteration
    310     * @param value given value
    311     * @param limit conflict limit
    312     * @return number of potential unassignments
    313     */
    314    public long countPotentialConflicts(Assignment<V, T> assignment, long iteration, T value, int limit) {
    315        iLock.readLock().lock();
    316        try {
    317            List<AssignedValue<T>> asss = iAssignments.get(new AssignedValue<T>(iteration, value, iAgeing));
    318            if (asss == null)
    319                return 0;
    320            long count = 0;
    321            for (AssignedValue<T> ass : asss) {
    322                if (ass.getValue().variable().getAssignment(assignment) == null) {
    323                    if (limit >= 0) {
    324                        count += ass.getCounter(iteration) * Math.max(0, 1 + limit - value.variable().getModel().conflictValues(assignment, ass.getValue()).size());
    325                    } else {
    326                        count += ass.getCounter(iteration);
    327                    }
    328                }
    329            }
    330            return count;
    331        } finally {
    332            iLock.readLock().unlock();
    333        }
    334    }
    335
    336    private int countAssignments(V variable) {
    337        iLock.readLock().lock();
    338        try {
    339            List<AssignedValue<T>> assignments = iUnassignedVariables.get(variable);
    340            if (assignments == null || assignments.isEmpty()) return 0;
    341            int ret = 0;
    342            for (AssignedValue<T> assignment: assignments) {
    343                ret += assignment.getCounter(0);
    344            }
    345            return ret;
    346        } finally {
    347            iLock.readLock().unlock();
    348        }
    349    }
    350
    351    @Override
    352    public String toString() {
    353        iLock.readLock().lock();
    354        try {
    355            if (iPrint) {
    356                StringBuffer sb = new StringBuffer("Statistics{");
    357                TreeSet<AssignedValue<T>> sortedUnassignments = new TreeSet<AssignedValue<T>>(new Comparator<AssignedValue<T>>() {
    358                    @Override
    359                    public int compare(AssignedValue<T> x1, AssignedValue<T> x2) {
    360                        int c1 = 0, c2 = 0;
    361                        for (AssignedValue<T> y: iNoGoods.get(x1))
    362                            c1 += y.getCounter(0);
    363                        for (AssignedValue<T> y: iNoGoods.get(x2))
    364                            c2 += y.getCounter(0);
    365                        int cmp = Double.compare(c1, c2);
    366                        if (cmp != 0)
    367                            return -cmp;
    368                        return x1.compareTo(0, x2);
    369                    }
    370                });
    371                sortedUnassignments.addAll(iNoGoods.keySet());
    372                int printedUnassignments = 0;
    373                for (AssignedValue<T> x : sortedUnassignments) {
    374                    int c = 0;
    375                    for (AssignedValue<T> y: iNoGoods.get(x))
    376                        c += y.getCounter(0);
    377                    sb.append("\n    ").append(c + "x ").append(x.toString(0, false)).append(" <= {");
    378                    TreeSet<AssignedValue<T>> sortedAssignments = new TreeSet<AssignedValue<T>>(new Comparator<AssignedValue<T>>() {
    379                        @Override
    380                        public int compare(AssignedValue<T> x1, AssignedValue<T> x2) {
    381                            int cmp = Double.compare(x1.getCounter(0), x2.getCounter(0));
    382                            if (cmp != 0)
    383                                return -cmp;
    384                            return x1.compareTo(0, x2);
    385                        }
    386                    });
    387                    sortedAssignments.addAll(iNoGoods.get(x));
    388                    int printedAssignments = 0;
    389                    for (AssignedValue<T> y : sortedAssignments) {
    390                        sb.append("\n        ").append(y.toString(0, true));
    391                        if (++printedAssignments == 20) {
    392                            sb.append("\n        ...");
    393                            break;
    394                        }
    395                    }
    396                    sb.append("\n      }");
    397                    if (++printedUnassignments == 100) {
    398                        sb.append("\n     ...");
    399                        break;
    400                    }
    401                }
    402                sb.append("\n    }");
    403                return sb.toString();
    404            } else {
    405                StringBuffer sb = new StringBuffer("Statistics{");
    406                TreeSet<V> sortedUnassignedVariables = new TreeSet<V>(new Comparator<V>() {
    407                    @Override
    408                    public int compare(V v1, V v2) {
    409                        int cmp = Double.compare(countAssignments(v1), countAssignments(v2));
    410                        if (cmp != 0)
    411                            return -cmp;
    412                        return v1.compareTo(v2);
    413                    }
    414                });
    415                sortedUnassignedVariables.addAll(iUnassignedVariables.keySet());
    416                int printedVariables = 0;
    417                for (V variable : sortedUnassignedVariables) {
    418                    sb.append("\n      ").append(countAssignments(variable) + "x ").append(variable.getName()).append(" <= {");
    419                    TreeSet<AssignedValue<T>> sortedAssignments = new TreeSet<AssignedValue<T>>(new Comparator<AssignedValue<T>>() {
    420                        @Override
    421                        public int compare(AssignedValue<T> x1, AssignedValue<T> x2) {
    422                            int cmp = Double.compare(x1.getCounter(0), x2.getCounter(0));
    423                            if (cmp != 0)
    424                                return -cmp;
    425                            return x1.compareTo(0, x2);
    426                        }
    427                    });
    428                    sortedAssignments.addAll(iUnassignedVariables.get(variable));
    429                    int printedAssignments = 0;
    430                    for (AssignedValue<T> x : sortedAssignments) {
    431                        sb.append("\n        ").append(x.toString(0, true));
    432                        if (++printedAssignments == 20) {
    433                            sb.append("\n        ...");
    434                            break;
    435                        }
    436                    }
    437                    sb.append("\n      }");
    438                    if (++printedVariables == 100) {
    439                        sb.append("\n      ...");
    440                        break;
    441                    }
    442                }
    443                sb.append("\n    }");
    444                return sb.toString();
    445            }
    446        } finally {
    447            iLock.readLock().unlock();
    448        }
    449    }
    450
    451    @Override
    452    public void constraintBeforeAssigned(Assignment<V, T> assignment, long iteration, Constraint<V, T> constraint, T assigned, Set<T> unassigned) {
    453    }
    454
    455    /** Increments appropriate counters when there is a value unassigned */
    456    @Override
    457    public void constraintAfterAssigned(Assignment<V, T> assignment, long iteration, Constraint<V, T> constraint, T assigned, Set<T> unassigned) {
    458        if (iteration <= 0)
    459            return;
    460        if (unassigned == null || unassigned.isEmpty())
    461            return;
    462        if (iPrint) {
    463            // AssignmentSet noGoods =
    464            // AssignmentSet.createAssignmentSet(iteration,unassigned, iAgeing);
    465            // noGoods.addAssignment(iteration, assigned, iAgeing);
    466            // noGoods.setConstraint(constraint);
    467            AssignedValue<T> noGood = new AssignedValue<T>(iteration, assigned, iAgeing);
    468            noGood.setConstraint(constraint);
    469            for (T unassignedValue : unassigned) {
    470                variableUnassigned(iteration, unassignedValue, noGood);
    471                variableUnassigned(iteration, unassignedValue, assigned);
    472            }
    473        } else {
    474            for (T unassignedValue : unassigned) {
    475                variableUnassigned(iteration, unassignedValue, assigned);
    476            }
    477        }
    478    }
    479
    480    @Override
    481    public void constraintAdded(Constraint<V, T> constraint) {
    482        constraint.addConstraintListener(this);
    483    }
    484
    485    @Override
    486    public void constraintRemoved(Constraint<V, T> constraint) {
    487        constraint.removeConstraintListener(this);
    488    }
    489}