1 /*******************************************************************************
2 * SAT4J: a SATisfiability library for Java Copyright (C) 2004, 2012 Artois University and CNRS
3 *
4 * All rights reserved. This program and the accompanying materials
5 * are made available under the terms of the Eclipse Public License v1.0
6 * which accompanies this distribution, and is available at
7 * http://www.eclipse.org/legal/epl-v10.html
8 *
9 * Alternatively, the contents of this file may be used under the terms of
10 * either the GNU Lesser General Public License Version 2.1 or later (the
11 * "LGPL"), in which case the provisions of the LGPL are applicable instead
12 * of those above. If you wish to allow use of your version of this file only
13 * under the terms of the LGPL, and not to allow others to use your version of
14 * this file under the terms of the EPL, indicate your decision by deleting
15 * the provisions above and replace them with the notice and other provisions
16 * required by the LGPL. If you do not delete the provisions above, a recipient
17 * may use your version of this file under the terms of the EPL or the LGPL.
18 *
19 * Based on the original MiniSat specification from:
20 *
21 * An extensible SAT solver. Niklas Een and Niklas Sorensson. Proceedings of the
22 * Sixth International Conference on Theory and Applications of Satisfiability
23 * Testing, LNCS 2919, pp 502-518, 2003.
24 *
25 * See www.minisat.se for the original solver in C++.
26 *
27 * Contributors:
28 * CRIL - initial API and implementation
29 *******************************************************************************/
30 package org.sat4j.tools.xplain;
31
32 import java.util.Map;
33 import java.util.Set;
34
35 import org.sat4j.core.VecInt;
36 import org.sat4j.specs.ISolver;
37 import org.sat4j.specs.IVecInt;
38 import org.sat4j.specs.IteratorInt;
39 import org.sat4j.specs.TimeoutException;
40
41 /**
42 * An implementation of the QuickXplain algorithm as explained by Ulrich Junker
43 * in the following paper:
44 *
45 * @inproceedings{ junker01:quickxplain:inp, author={Ulrich Junker},
46 * title={QUICKXPLAIN: Conflict Detection for Arbitrary
47 * Constraint Propagation Algorithms}, booktitle={IJCAI'01
48 * Workshop on Modelling and Solving problems with constraints
49 * (CONS-1)}, year={2001}, month={August}, address={Seattle, WA,
50 * USA}, url={citeseer.ist.psu.edu/junker01quickxplain.html},
51 * url={http://www.lirmm.fr/~bessiere/ws_ijcai01/junker.ps.gz} }
52 *
53 * The algorithm has been adapted to work properly in a context
54 * where we can afford to add a selector variable to each clause
55 * to enable or disable each constraint.
56 *
57 * Note that for the moment, QuickXplain does not work properly
58 * in an optimization setting.
59 *
60 *
61 * @since 2.1
62 */
63 public class QuickXplain2001Strategy implements MinimizationStrategy {
64
65 /**
66 *
67 */
68 private static final long serialVersionUID = 1L;
69
70 private boolean computationCanceled;
71
72 public void cancelExplanationComputation() {
73 this.computationCanceled = true;
74 }
75
76 public IVecInt explain(ISolver solver, Map<Integer, ?> constrs,
77 IVecInt assumps) throws TimeoutException {
78 this.computationCanceled = false;
79 IVecInt encodingAssumptions = new VecInt(constrs.size()
80 + assumps.size());
81 assumps.copyTo(encodingAssumptions);
82 IVecInt firstExplanation = solver.unsatExplanation();
83 if (solver.isVerbose()) {
84 System.out.print(solver.getLogPrefix() + "initial unsat core ");
85 firstExplanation.sort();
86 for (IteratorInt it = firstExplanation.iterator(); it.hasNext();) {
87 System.out.print(constrs.get(-it.next()));
88 System.out.print(" ");
89 }
90 System.out.println();
91 }
92 Set<Integer> constraintsVariables = constrs.keySet();
93 int p;
94 for (int i = 0; i < firstExplanation.size(); i++) {
95 if (constraintsVariables.contains(p = -firstExplanation.get(i))) {
96 encodingAssumptions.push(p);
97 }
98 }
99 IVecInt results = new VecInt(encodingAssumptions.size());
100 computeExplanation(solver, encodingAssumptions, assumps.size(),
101 encodingAssumptions.size() - 1, results);
102 return results;
103 }
104
105 private void computeExplanation(ISolver solver,
106 IVecInt encodingAssumptions, int start, int end, IVecInt result)
107 throws TimeoutException {
108 if (!solver.isSatisfiable(encodingAssumptions)) {
109 return;
110 }
111 int i = start;
112 encodingAssumptions.set(i, -encodingAssumptions.get(i));
113 assert encodingAssumptions.get(i) < 0;
114 while (!this.computationCanceled
115 && solver.isSatisfiable(encodingAssumptions)) {
116 if (i == end) {
117 for (int j = start; j <= end; j++) {
118 encodingAssumptions.set(j, -encodingAssumptions.get(j));
119 }
120 return;
121 }
122 i++;
123 assert encodingAssumptions.get(i) > 0;
124 encodingAssumptions.set(i, -encodingAssumptions.get(i));
125 }
126 result.push(-encodingAssumptions.get(i));
127 if (start == i) {
128 return;
129 }
130 int newend = i - 1;
131 int split = (newend + start) / 2;
132 if (split < newend) {
133 for (int j = split + 1; j < i; j++) {
134 encodingAssumptions.set(j, -encodingAssumptions.get(j));
135 }
136 computeExplanation(solver, encodingAssumptions, split + 1, newend,
137 result);
138 }
139 if (start <= split) {
140 for (int j = start; j <= split; j++) {
141 encodingAssumptions.set(j, -encodingAssumptions.get(j));
142 }
143 computeExplanation(solver, encodingAssumptions, start, split,
144 result);
145 }
146 if (this.computationCanceled) {
147 throw new TimeoutException();
148 }
149 }
150
151 @Override
152 public String toString() {
153 return "QuickXplain (IJCAI WS 2001 version) minimization strategy";
154 }
155 }