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.minisat.uip;
29
30 import java.io.Serializable;
31
32 import org.sat4j.minisat.core.AssertingClauseGenerator;
33 import org.sat4j.specs.IConstr;
34
35 /**
36 * FirstUIP scheme introduced in Chaff. Here the generator stops when a
37 * syntactical criteria is met: only one literal in the current decision level
38 * appears in the generated clause. The computation is done by counting the
39 * literals appearing in the current decision level and decrementing that
40 * counter when a resolution step is done.
41 *
42 * @author leberre
43 */
44 public class FirstUIP implements AssertingClauseGenerator, Serializable {
45
46 private static final long serialVersionUID = 1L;
47
48 private int counter;
49
50 public void initAnalyze() {
51 counter = 0;
52 }
53
54 public void onCurrentDecisionLevelLiteral(int p) {
55 counter++;
56 }
57
58 public boolean clauseNonAssertive(IConstr reason) {
59 return --counter > 0;
60 }
61
62 @Override
63 public String toString() {
64 return "Stops conflict analysis at the first Unique Implication Point";
65 }
66
67 }