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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.core;
29  
30  import java.io.Serializable;
31  
32  /**
33   * The responsibility of that class is to choose the phase (positive or
34   * negative) of the variable that was selected by the IOrder.
35   * 
36   * @author leberre
37   * 
38   */
39  public interface IPhaseSelectionStrategy extends Serializable {
40  
41  	/**
42  	 * To be called when the activity of a literal changed.
43  	 * 
44  	 * @param p
45  	 *            a literal. The associated variable will be updated.
46  	 */
47  	void updateVar(int p);
48  
49  	/**
50  	 * that method has the responsibility to initialize all arrays in the
51  	 * heuristics.
52  	 * 
53  	 * @param nlength
54  	 *            the number of variables managed by the heuristics.
55  	 */
56  	void init(int nlength);
57  
58  	/**
59  	 * initialize the phase of a given variable to the given value. That method
60  	 * is suppose to be called AFTER init(int).
61  	 * 
62  	 * @param var
63  	 *            a variable
64  	 * @param p
65  	 *            it's initial phase
66  	 */
67  	void init(int var, int p);
68  
69  	/**
70  	 * indicate that a literal has been satisfied.
71  	 * 
72  	 * @param p
73  	 */
74  	void assignLiteral(int p);
75  
76  	/**
77  	 * selects the phase of the variable according to a phase selection
78  	 * strategy.
79  	 * 
80  	 * @param var
81  	 *            a variable chosen by the heuristics
82  	 * @return either var or not var, depending of the selection strategy.
83  	 * 
84  	 */
85  	int select(int var);
86  
87  	/**
88  	 * Allow to perform a specific action when a literal of the current decision
89  	 * level is updated. That method is called after {@link #updateVar(int)}.
90  	 * 
91  	 * @param q
92  	 *            a literal
93  	 */
94  	void updateVarAtDecisionLevel(int q);
95  }