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.io.Serializable;
31 import java.math.BigInteger;
32
33 import org.sat4j.core.ReadOnlyVec;
34 import org.sat4j.core.ReadOnlyVecInt;
35 import org.sat4j.specs.IVec;
36 import org.sat4j.specs.IVecInt;
37
38 /**
39 * Abstraction for an Objective Function for Pseudo Boolean Optimization.
40 *
41 * May be generalized in the future to deal with other optimization functions.
42 *
43 * @author leberre
44 *
45 */
46 public class ObjectiveFunction implements Serializable {
47
48 /**
49 *
50 */
51 private static final long serialVersionUID = 1L;
52
53 // contains the coeffs of the objective function for each variable
54 private final IVec<BigInteger> coeffs;
55
56 private final IVecInt vars;
57
58 public ObjectiveFunction(IVecInt vars, IVec<BigInteger> coeffs) {
59 this.vars = new ReadOnlyVecInt(vars);
60 this.coeffs = new ReadOnlyVec<BigInteger>(coeffs);
61 }
62
63 // calculate the degree of the objective function
64 public BigInteger calculateDegree(int[] model) {
65 BigInteger tempDegree = BigInteger.ZERO;
66
67 for (int i = 0; i < vars.size(); i++) {
68 BigInteger coeff = coeffs.get(i);
69 if (varInModel(vars.get(i), model))
70 tempDegree = tempDegree.add(coeff);
71 else if ((coeff.signum()<0)&&!varInModel(-vars.get(i), model)) {
72 // the variable does not appear in the model: it can be assigned either way
73 // System.out.println("c special optimisation obj. function for var "+i);
74 tempDegree = tempDegree.add(coeff);
75 }
76 }
77 return tempDegree;
78 }
79
80 private boolean varInModel(int var, int[] model) {
81 for (int i = 0; i < model.length; i++)
82 if (var == model[i])
83 return true;
84 return false;
85 }
86
87 public IVec<BigInteger> getCoeffs() {
88 return coeffs;
89 }
90
91 public IVecInt getVars() {
92 return vars;
93 }
94
95 }