1 /*******************************************************************************
2 * SAT4J: a SATisfiability library for Java Copyright (C) 2004-2008 Daniel Le Berre
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 *******************************************************************************/
28 package org.sat4j.tools;
29
30 import org.sat4j.core.VecInt;
31 import org.sat4j.specs.ISolver;
32 import org.sat4j.specs.IVecInt;
33 import org.sat4j.specs.TimeoutException;
34
35 /**
36 * Class dedicated to Remi Coletta utility methods :-)
37 *
38 * @author leberre
39 */
40 public final class RemiUtils {
41
42 private RemiUtils() {
43 // no instanceof that class are expected to be used.
44 }
45
46 /**
47 * Compute the set of literals common to all models of the formula.
48 *
49 * @param s
50 * a solver already feeded
51 * @return the set of literals common to all models of the formula contained
52 * in the solver, in dimacs format.
53 * @throws TimeoutException
54 */
55 public static IVecInt backbone(ISolver s) throws TimeoutException {
56 IVecInt backbone = new VecInt();
57 int nvars = s.nVars();
58 for (int i = 1; i <= nvars; i++) {
59 backbone.push(i);
60 if (s.isSatisfiable(backbone)) {
61 backbone.pop().push(-i);
62 if (s.isSatisfiable(backbone)) {
63 backbone.pop();
64 } else {
65 // -i is in the backbone
66 backbone.pop().push(i);
67 }
68 } else {
69 // -i is in the backbone
70 backbone.pop().push(-i);
71 }
72 }
73 return backbone;
74 }
75
76 }