1 /*
2 * SAT4J: a SATisfiability library for Java Copyright (C) 2004-2006 Daniel Le Berre
3 *
4 * Based on the original minisat specification from:
5 *
6 * An extensible SAT solver. Niklas E?n and Niklas S?rensson. Proceedings of the
7 * Sixth International Conference on Theory and Applications of Satisfiability
8 * Testing, LNCS 2919, pp 502-518, 2003.
9 *
10 * This library is free software; you can redistribute it and/or modify it under
11 * the terms of the GNU Lesser General Public License as published by the Free
12 * Software Foundation; either version 2.1 of the License, or (at your option)
13 * any later version.
14 *
15 * This library is distributed in the hope that it will be useful, but WITHOUT
16 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
17 * FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License for more
18 * details.
19 *
20 * You should have received a copy of the GNU Lesser General Public License
21 * along with this library; if not, write to the Free Software Foundation, Inc.,
22 * 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
23 *
24 */
25 package org.sat4j.tools;
26
27 import org.sat4j.core.VecInt;
28 import org.sat4j.specs.ISolver;
29 import org.sat4j.specs.IVecInt;
30 import org.sat4j.specs.TimeoutException;
31
32 /**
33 * Class dedicated to Remi Coletta utility methods :-)
34 *
35 * @author leberre
36 */
37 public class RemiUtils {
38
39 private RemiUtils() {
40 // no instanceof that class are expected to be used.
41 }
42
43 /**
44 * Compute the set of literals common to all models of the formula.
45 *
46 * @param s
47 * a solver already feeded
48 * @return the set of literals common to all models of the formula contained
49 * in the solver, in dimacs format.
50 * @throws TimeoutException
51 */
52 public static IVecInt backbone(ISolver s) throws TimeoutException {
53 IVecInt backbone = new VecInt();
54 int nvars = s.nVars();
55 for (int i = 1; i <= nvars; i++) {
56 backbone.push(i);
57 if (s.isSatisfiable(backbone)) {
58 backbone.pop().push(-i);
59 if (s.isSatisfiable(backbone)) {
60 backbone.pop();
61 } else {
62 // -i is in the backbone
63 backbone.pop().push(i);
64 }
65 } else {
66 // -i is in the backbone
67 backbone.pop().push(-i);
68 }
69 }
70 return backbone;
71 }
72
73 }