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 pseudo boolean algorithms described in:
20 * A fast pseudo-Boolean constraint solver Chai, D.; Kuehlmann, A.
21 * Computer-Aided Design of Integrated Circuits and Systems, IEEE Transactions on
22 * Volume 24, Issue 3, March 2005 Page(s): 305 - 317
23 *
24 * and
25 * Heidi E. Dixon, 2004. Automating Pseudo-Boolean Inference within a DPLL
26 * Framework. Ph.D. Dissertation, University of Oregon.
27 *******************************************************************************/
28 package org.sat4j.pb;
29
30 import java.math.BigInteger;
31
32 import org.sat4j.specs.ContradictionException;
33 import org.sat4j.specs.IOptimizationProblem;
34 import org.sat4j.specs.TimeoutException;
35
36 /**
37 * A decorator that computes minimal pseudo boolean models.
38 *
39 * @author daniel
40 *
41 */
42 public class PseudoOptDecorator extends PBSolverDecorator implements
43 IOptimizationProblem {
44
45 /**
46 *
47 */
48 private static final long serialVersionUID = 1L;
49
50 private ObjectiveFunction objfct;
51
52 private int[] prevmodel;
53 private boolean[] prevfullmodel;
54
55 public PseudoOptDecorator(IPBSolver solver) {
56 super(solver);
57 }
58
59 @Override
60 public void setObjectiveFunction(ObjectiveFunction objf) {
61 objfct = objf;
62 decorated().setObjectiveFunction(objf);
63 }
64
65 public boolean admitABetterSolution() throws TimeoutException {
66 boolean result = super.isSatisfiable(true);
67 if (result) {
68 prevmodel = super.model();
69 prevfullmodel = new boolean[nVars()];
70 for (int i=0;i<nVars();i++) {
71 prevfullmodel[i]=decorated().model(i+1);
72 }
73 }
74 return result;
75 }
76
77 public boolean hasNoObjectiveFunction() {
78 return objfct == null;
79 }
80
81 public boolean nonOptimalMeansSatisfiable() {
82 return true;
83 }
84
85 public Number calculateObjective() {
86 return objfct.calculateDegree(prevmodel);
87 }
88
89 public void discard() throws ContradictionException {
90 super.addPseudoBoolean(objfct.getVars(), objfct.getCoeffs(), false,
91 objfct.calculateDegree(prevmodel).subtract(BigInteger.ONE));
92 }
93
94 @Override
95 public int[] model() {
96 // DLB findbugs ok
97 return prevmodel;
98 }
99
100 @Override
101 public boolean model(int var) {
102 return prevfullmodel[var-1];
103 }
104
105 @Override
106 public String toString(String prefix) {
107 return prefix+"Pseudo Boolean Optimization\n"+super.toString(prefix);
108 }
109
110
111
112 }