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.PrintWriter;
31
32 /**
33 * Interface for the variable ordering heuristics. It has both the
34 * responsibility to choose the next variable to branch on and the phase of the
35 * literal (positive or negative one).
36 *
37 * @author daniel
38 *
39 */
40 public interface IOrder {
41
42 /**
43 * Method used to provide an easy access the the solver vocabulary.
44 *
45 * @param lits
46 * the vocabulary
47 */
48 void setLits(ILits lits);
49
50 /**
51 * Selects the next "best" unassigned literal.
52 *
53 * Note that it means selecting the best variable and the phase to branch on
54 * first.
55 *
56 * @return an unassigned literal or Lit.UNDEFINED no such literal exists.
57 */
58 int select();
59
60 /**
61 * Method called when a variable is unassigned.
62 *
63 * It is useful to add back a variable in the pool of variables to order.
64 *
65 * @param x
66 * a variable.
67 */
68 void undo(int x);
69
70 /**
71 * To be called when the activity of a literal changed.
72 *
73 * @param p
74 * a literal. The associated variable will be updated.
75 */
76 void updateVar(int p);
77
78 /**
79 * that method has the responsibility to initialize all arrays in the
80 * heuristics. PLEASE CALL super.init() IF YOU OVERRIDE THAT METHOD.
81 */
82 void init();
83
84 /**
85 * Display statistics regarding the heuristics.
86 *
87 * @param out
88 * the writer to display the information in
89 * @param prefix
90 * to be used in front of each newline.
91 */
92 void printStat(PrintWriter out, String prefix);
93
94 /**
95 * Sets the variable activity decay as a growing factor for the next
96 * variable activity.
97 *
98 * @param d
99 * a number bigger than 1 that will increase the activity of the
100 * variables involved in future conflict. This is similar but
101 * more efficient than decaying all the activities by a similar
102 * factor.
103 */
104 void setVarDecay(double d);
105
106 /**
107 * Decay the variables activities.
108 *
109 */
110 void varDecayActivity();
111
112 /**
113 * To obtain the current activity of a variable.
114 *
115 * @param p
116 * a literal
117 * @return the activity of the variable associated to that literal.
118 */
119 double varActivity(int p);
120
121 /**
122 * indicate that a literal has been satisfied.
123 *
124 * @param p
125 */
126 void assignLiteral(int p);
127
128 void setPhaseSelectionStrategy(IPhaseSelectionStrategy strategy);
129
130 IPhaseSelectionStrategy getPhaseSelectionStrategy();
131
132 /**
133 * Allow to perform a specific action when a literal of the current decision
134 * level is updated. That method is called after {@link #updateVar(int)}.
135 *
136 * @param q
137 * a literal
138 */
139 void updateVarAtDecisionLevel(int q);
140 }