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.orders;
29
30 import static org.sat4j.core.LiteralsUtils.neg;
31 import static org.sat4j.core.LiteralsUtils.var;
32
33 import java.io.PrintWriter;
34 import java.io.Serializable;
35
36 import org.sat4j.minisat.core.ILits;
37 import org.sat4j.minisat.core.IOrder;
38 import org.sat4j.minisat.core.IPhaseSelectionStrategy;
39
40 /*
41 * Created on 16 oct. 2003
42 */
43
44 /**
45 * @author leberre Heuristique du prouveur. Changement par rapport au MiniSAT
46 * original : la gestion activity est faite ici et non plus dans Solver.
47 */
48 public class VarOrder<L extends ILits> implements Serializable, IOrder<L> {
49
50 private static final long serialVersionUID = 1L;
51
52 /**
53 * Comparateur permettant de trier les variables
54 */
55 private static final double VAR_RESCALE_FACTOR = 1e-100;
56
57 private static final double VAR_RESCALE_BOUND = 1 / VAR_RESCALE_FACTOR;
58
59 /**
60 * mesure heuristique de l'activite d'une variable.
61 */
62 protected double[] activity = new double[1];
63
64 /**
65 * Derniere variable choisie
66 */
67 protected int lastVar = 1;
68
69 /**
70 * Ordre des variables
71 */
72 protected int[] order = new int[1];
73
74 private double varDecay = 1.0;
75
76 /**
77 * increment pour l'activite des variables.
78 */
79 private double varInc = 1.0;
80
81 /**
82 * position des variables
83 */
84 protected int[] varpos = new int[1];
85
86 protected L lits;
87
88 private long nullchoice = 0;
89
90 protected IPhaseSelectionStrategy phaseStrategy;
91
92 public VarOrder() {
93 this(new PhaseInLastLearnedClauseSelectionStrategy());
94 }
95
96 public VarOrder(IPhaseSelectionStrategy strategy) {
97 this.phaseStrategy = strategy;
98 }
99
100 /**
101 * Change the selection strategy.
102 *
103 * @param strategy
104 */
105 public void setPhaseSelectionStrategy(IPhaseSelectionStrategy strategy) {
106 phaseStrategy = strategy;
107 }
108
109 public IPhaseSelectionStrategy getPhaseSelectionStrategy() {
110 return phaseStrategy;
111 }
112
113 /*
114 * (non-Javadoc)
115 *
116 * @see org.sat4j.minisat.core.IOrder#setLits(org.sat4j.minisat.core.ILits)
117 */
118 public void setLits(L lits) {
119 this.lits = lits;
120 }
121
122 /*
123 * (non-Javadoc)
124 *
125 * @see org.sat4j.minisat.core.IOrder#select()
126 */
127 public int select() {
128 assert lastVar > 0;
129 for (int i = lastVar; i < order.length; i++) {
130 assert i > 0;
131 if (lits.isUnassigned(order[i])) {
132 lastVar = i;
133 if (activity[i] < 0.0001) {
134 // if (rand.nextDouble() <= RANDOM_WALK) {
135 // int randomchoice = rand.nextInt(order.length - i) + i;
136 // assert randomchoice >= i;
137 // if ((randomchoice > i)
138 // && lits.isUnassigned(order[randomchoice])) {
139 // randchoice++;
140 // return order[randomchoice];
141 // }
142 // }
143 nullchoice++;
144 }
145 return order[i];
146 }
147 }
148 return ILits.UNDEFINED;
149 }
150
151 /**
152 * Change la valeur de varDecay.
153 *
154 * @param d
155 * la nouvelle valeur de varDecay
156 */
157 public void setVarDecay(double d) {
158 varDecay = d;
159 }
160
161 /*
162 * (non-Javadoc)
163 *
164 * @see org.sat4j.minisat.core.IOrder#undo(int)
165 */
166 public void undo(int x) {
167 assert x > 0;
168 assert x < order.length;
169 int pos = varpos[x];
170 if (pos < lastVar) {
171 lastVar = pos;
172 }
173 assert lastVar > 0;
174 }
175
176 /*
177 * (non-Javadoc)
178 *
179 * @see org.sat4j.minisat.core.IOrder#updateVar(int)
180 */
181 public void updateVar(int p) {
182 assert p > 1;
183 final int var = var(p);
184
185 updateActivity(var);
186 int i = varpos[var];
187 for (; i > 1 // because there is nothing at i=0
188 && (activity[var(order[i - 1])] < activity[var]); i--) {
189 assert i > 1;
190 // echange p avec son predecesseur
191 final int orderpm1 = order[i - 1];
192 assert varpos[var(orderpm1)] == i - 1;
193 varpos[var(orderpm1)] = i;
194 order[i] = orderpm1;
195 }
196 assert i >= 1;
197 varpos[var] = i;
198 order[i] = p;
199
200 if (i < lastVar) {
201 lastVar = i;
202 }
203 }
204
205 protected void updateActivity(final int var) {
206 if ((activity[var] += varInc) > VAR_RESCALE_BOUND) {
207 varRescaleActivity();
208 }
209 }
210
211 /**
212 *
213 */
214 public void varDecayActivity() {
215 varInc *= varDecay;
216 }
217
218 /**
219 *
220 */
221 private void varRescaleActivity() {
222 for (int i = 1; i < activity.length; i++) {
223 activity[i] *= VAR_RESCALE_FACTOR;
224 }
225 varInc *= VAR_RESCALE_FACTOR;
226 }
227
228 public double varActivity(int p) {
229 return activity[var(p)];
230 }
231
232 /**
233 *
234 */
235 public int numberOfInterestingVariables() {
236 int cpt = 0;
237 for (int i = 1; i < activity.length; i++) {
238 if (activity[i] > 1.0) {
239 cpt++;
240 }
241 }
242 return cpt;
243 }
244
245 /*
246 * (non-Javadoc)
247 *
248 * @see org.sat4j.minisat.core.IOrder#init()
249 */
250 public void init() {
251 int nlength = lits.nVars() + 1;
252 int reallength = lits.realnVars() + 1;
253 int[] nvarpos = new int[nlength];
254 double[] nactivity = new double[nlength];
255 int[] norder = new int[reallength];
256 nvarpos[0] = -1;
257 nactivity[0] = -1;
258 norder[0] = ILits.UNDEFINED;
259 for (int i = 1, j = 1; i < nlength; i++) {
260 assert i > 0;
261 assert i <= lits.nVars() : "" + lits.nVars() + "/" + i; //$NON-NLS-1$ //$NON-NLS-2$
262 if (lits.belongsToPool(i)) {
263 norder[j] = neg(lits.getFromPool(i)); // Looks a
264 // promising
265 // approach
266 nvarpos[i] = j++;
267 }
268 nactivity[i] = 0.0;
269 }
270 varpos = nvarpos;
271 activity = nactivity;
272 order = norder;
273 lastVar = 1;
274 }
275
276 /**
277 * Affiche les litteraux dans l'ordre de l'heuristique, la valeur de
278 * l'activite entre ().
279 *
280 * @return les litteraux dans l'ordre courant.
281 */
282 @Override
283 public String toString() {
284 return "VSIDS like heuristics from MiniSAT using a sorted array"; //$NON-NLS-1$
285 }
286
287 public ILits getVocabulary() {
288 return lits;
289 }
290
291 /*
292 * (non-Javadoc)
293 *
294 * @see org.sat4j.minisat.core.IOrder#printStat(java.io.PrintStream,
295 * java.lang.String)
296 */
297 public void printStat(PrintWriter out, String prefix) {
298 out.println(prefix + "non guided choices\t" + nullchoice); //$NON-NLS-1$
299 // out.println(prefix + "random choices\t" + randchoice);
300 }
301
302 public void assignLiteral(int p) {
303 // do nothing
304 }
305
306 }