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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.minisat.orders;
31  
32  import static org.sat4j.core.LiteralsUtils.negLit;
33  import static org.sat4j.core.LiteralsUtils.posLit;
34  
35  import java.util.Random;
36  
37  import org.sat4j.minisat.core.IPhaseSelectionStrategy;
38  
39  /**
40   * The variable selection strategy randomly picks one phase, either positive or
41   * negative.
42   * 
43   * @author leberre
44   * 
45   */
46  public final class RandomLiteralSelectionStrategy implements
47          IPhaseSelectionStrategy {
48  
49      /**
50       * 
51       */
52      private static final long serialVersionUID = 1L;
53  
54      /**
55       * @since 2.2
56       */
57      public static final Random RAND = new Random(123456789);
58  
59      public void assignLiteral(int p) {
60      }
61  
62      public void init(int nlength) {
63      }
64  
65      public void init(int var, int p) {
66      }
67  
68      public int select(int var) {
69          if (RAND.nextBoolean()) {
70              return posLit(var);
71          }
72          return negLit(var);
73      }
74  
75      public void updateVar(int p) {
76      }
77  
78      public void updateVarAtDecisionLevel(int q) {
79      }
80  
81      @Override
82      public String toString() {
83          return "random phase selection";
84      }
85  }