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.restarts;
31
32 import org.sat4j.minisat.core.Constr;
33 import org.sat4j.minisat.core.RestartStrategy;
34 import org.sat4j.minisat.core.SearchParams;
35
36 /**
37 * Luby series
38 */
39 public final class LubyRestarts implements RestartStrategy {
40
41 public static final int DEFAULT_LUBY_FACTOR = 32;
42
43 /**
44 *
45 */
46 private static final long serialVersionUID = 1L;
47
48 // 21-06-2012 back from SAT 2012
49 // computing luby values the way presented by Donald Knuth in his invited
50 // talk at the SAT 2012 conference
51 // u1
52 private int un = 1;
53 // v1
54 private int vn = 1;
55
56 /**
57 * returns the current value of the luby sequence.
58 *
59 * @return the current value of the luby sequence.
60 */
61 public int luby() {
62 return this.vn;
63 }
64
65 /**
66 * Computes and return the next value of the luby sequence. That method has
67 * a side effect of the value returned by luby(). luby()!=nextLuby() but
68 * nextLuby()==luby().
69 *
70 * @return the new current value of the luby sequence.
71 * @see #luby()
72 */
73 public int nextLuby() {
74 if ((this.un & -this.un) == this.vn) {
75 this.un = this.un + 1;
76 this.vn = 1;
77 } else {
78 this.vn = this.vn << 1;
79 }
80 return this.vn;
81 }
82
83 private int factor;
84
85 private int bound;
86 private int conflictcount;
87
88 public LubyRestarts() {
89 this(DEFAULT_LUBY_FACTOR); // uses TiniSAT default
90 }
91
92 /**
93 * @param factor
94 * the factor used for the Luby series.
95 * @since 2.1
96 */
97 public LubyRestarts(int factor) {
98 setFactor(factor);
99 }
100
101 public final void setFactor(int factor) {
102 this.factor = factor;
103 }
104
105 public int getFactor() {
106 return this.factor;
107 }
108
109 public void init(SearchParams params) {
110 this.un = 1;
111 this.vn = 1;
112 this.bound = luby() * this.factor;
113 }
114
115 public long nextRestartNumberOfConflict() {
116 return this.bound;
117 }
118
119 public void onRestart() {
120 this.bound = nextLuby() * this.factor;
121 this.conflictcount = 0;
122 }
123
124 @Override
125 public String toString() {
126 return "luby style (SATZ_rand, TiniSAT) restarts strategy with factor "
127 + this.factor;
128 }
129
130 public boolean shouldRestart() {
131 return this.conflictcount >= this.bound;
132 }
133
134 public void onBackjumpToRootLevel() {
135 this.conflictcount = 0;
136 }
137
138 public void reset() {
139 this.conflictcount = 0;
140 }
141
142 public void newConflict() {
143 this.conflictcount++;
144 }
145
146 public SearchParams getSearchParams() {
147 return new SearchParams();
148 }
149
150 public void newLearnedClause(Constr learned, int trailLevel) {
151 }
152 }