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.core;
31
32 import java.io.PrintWriter;
33
34 /**
35 * Interface for the variable ordering heuristics. It has both the
36 * responsibility to choose the next variable to branch on and the phase of the
37 * literal (positive or negative one).
38 *
39 * @author daniel
40 *
41 */
42 public interface IOrder {
43
44 /**
45 * Method used to provide an easy access the the solver vocabulary.
46 *
47 * @param lits
48 * the vocabulary
49 */
50 void setLits(ILits lits);
51
52 /**
53 * Selects the next "best" unassigned literal.
54 *
55 * Note that it means selecting the best variable and the phase to branch on
56 * first.
57 *
58 * @return an unassigned literal or Lit.UNDEFINED no such literal exists.
59 */
60 int select();
61
62 /**
63 * Method called when a variable is unassigned.
64 *
65 * It is useful to add back a variable in the pool of variables to order.
66 *
67 * @param x
68 * a variable.
69 */
70 void undo(int x);
71
72 /**
73 * To be called when the activity of a literal changed.
74 *
75 * @param p
76 * a literal. The associated variable will be updated.
77 */
78 void updateVar(int p);
79
80 /**
81 * that method has the responsibility to initialize all arrays in the
82 * heuristics. PLEASE CALL super.init() IF YOU OVERRIDE THAT METHOD.
83 */
84 void init();
85
86 /**
87 * Display statistics regarding the heuristics.
88 *
89 * @param out
90 * the writer to display the information in
91 * @param prefix
92 * to be used in front of each newline.
93 */
94 void printStat(PrintWriter out, String prefix);
95
96 /**
97 * Sets the variable activity decay as a growing factor for the next
98 * variable activity.
99 *
100 * @param d
101 * a number bigger than 1 that will increase the activity of the
102 * variables involved in future conflict. This is similar but
103 * more efficient than decaying all the activities by a similar
104 * factor.
105 */
106 void setVarDecay(double d);
107
108 /**
109 * Decay the variables activities.
110 *
111 */
112 void varDecayActivity();
113
114 /**
115 * To obtain the current activity of a variable.
116 *
117 * @param p
118 * a literal
119 * @return the activity of the variable associated to that literal.
120 */
121 double varActivity(int p);
122
123 /**
124 * indicate that a literal has been satisfied.
125 *
126 * @param p
127 */
128 void assignLiteral(int p);
129
130 void setPhaseSelectionStrategy(IPhaseSelectionStrategy strategy);
131
132 IPhaseSelectionStrategy getPhaseSelectionStrategy();
133
134 /**
135 * Allow to perform a specific action when a literal of the current decision
136 * level is updated. That method is called after {@link #updateVar(int)}.
137 *
138 * @param q
139 * a literal
140 */
141 void updateVarAtDecisionLevel(int q);
142
143 /**
144 * Read-Only access to the value of the heuristics for each variable. Note
145 * that for efficiency reason, the real array storing the value of the
146 * heuristics is returned. DO NOT CHANGE THE VALUES IN THAT ARRAY.
147 *
148 * @return the value of the heuristics for each variable (using Dimacs
149 * index).
150 * @since 2.3.2
151 */
152 double[] getVariableHeuristics();
153 }