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.specs;
29
30 /**
31 * Represents an optimization problem. The SAT solver will find suboptimal
32 * solutions of the problem until no more solutions are available. The latest
33 * solution found will be the optimal one.
34 *
35 * Such kind of problem is supposed to be handled:
36 *
37 * <pre>
38 * boolean isSatisfiable = false;
39 *
40 * IOptimizationProblem optproblem = (IOptimizationProblem) problem;
41 *
42 * try {
43 * while (optproblem.admitABetterSolution()) {
44 * if (!isSatisfiable) {
45 * if (optproblem.nonOptimalMeansSatisfiable()) {
46 * setExitCode(ExitCode.SATISFIABLE);
47 * if (optproblem.hasNoObjectiveFunction()) {
48 * return;
49 * }
50 * log("SATISFIABLE"); //$NON-NLS-1$
51 * }
52 * isSatisfiable = true;
53 * log("OPTIMIZING..."); //$NON-NLS-1$
54 * }
55 * log("Got one! Elapsed wall clock time (in seconds):" //$NON-NLS-1$
56 * + (System.currentTimeMillis() - getBeginTime()) / 1000.0);
57 * getLogWriter().println(
58 * CURRENT_OPTIMUM_VALUE_PREFIX + optproblem.getObjectiveValue());
59 * optproblem.discardCurrentSolution();
60 * }
61 * if (isSatisfiable) {
62 * setExitCode(ExitCode.OPTIMUM_FOUND);
63 * } else {
64 * setExitCode(ExitCode.UNSATISFIABLE);
65 * }
66 * } catch (ContradictionException ex) {
67 * assert isSatisfiable;
68 * setExitCode(ExitCode.OPTIMUM_FOUND);
69 * }
70 * </pre>
71 *
72 * @author leberre
73 *
74 */
75 public interface IOptimizationProblem extends IProblem {
76
77 /**
78 * Look for a solution of the optimization problem.
79 *
80 * @return true if a better solution than current one can be found.
81 * @throws TimeoutException
82 * if the solver cannot answer in reasonable time.
83 * @see ISolver#setTimeout(int)
84 */
85 boolean admitABetterSolution() throws TimeoutException;
86
87 /**
88 * Look for a solution of the optimization problem when some literals are
89 * satisfied.
90 *
91 * @param assumps
92 * a set of literals in Dimacs format.
93 * @return true if a better solution than current one can be found.
94 * @throws TimeoutException
95 * if the solver cannot answer in reasonable time.
96 * @see ISolver#setTimeout(int)
97 * @since 2.1
98 */
99 boolean admitABetterSolution(IVecInt assumps) throws TimeoutException;
100
101 /**
102 * If the optimization problem has no objective function, then it is a
103 * simple decision problem.
104 *
105 * @return true if the problem is a decision problem, false if the problem
106 * is an optimization problem.
107 */
108 boolean hasNoObjectiveFunction();
109
110 /**
111 * A suboptimal solution has different meaning depending of the optimization
112 * problem considered.
113 *
114 * For instance, in the case of MAXSAT, a suboptimal solution does not mean
115 * that the problem is satisfiable, while in pseudo boolean optimization, it
116 * is true.
117 *
118 * @return true if founding a suboptimal solution means that the problem is
119 * satisfiable.
120 */
121 boolean nonOptimalMeansSatisfiable();
122
123 /**
124 * Compute the value of the objective function for the current solution. A
125 * call to that method only makes sense if hasNoObjectiveFunction()==false.
126 *
127 * DO NOT CALL THAT METHOD THAT WILL BE CALLED AUTOMATICALLY. USE
128 * getObjectiveValue() instead!
129 *
130 * @return the value of the objective function.
131 * @see #getObjectiveValue()
132 */
133 @Deprecated
134 Number calculateObjective();
135
136 /**
137 * Read only access to the value of the objective function for the current
138 * solution.
139 *
140 * @return the value of the objective function for the current solution.
141 * @since 2.1
142 */
143 Number getObjectiveValue();
144
145 /**
146 * Force the value of the objective function.
147 *
148 * This is especially useful to iterate over optimal solutions.
149 *
150 * @throws ContradictionException
151 * @since 2.1
152 */
153 void forceObjectiveValueTo(Number forcedValue)
154 throws ContradictionException;
155
156 /**
157 * Discard the current solution in the optimization problem.
158 *
159 * THE NAME WAS NOT NICE. STILL AVAILABLE TO AVOID BREAKING THE API. PLEASE
160 * USE THE LONGER discardCurrentSolution() instead.
161 *
162 * @throws ContradictionException
163 * if a trivial inconsistency is detected.
164 * @see #discardCurrentSolution()
165 */
166 @Deprecated
167 void discard() throws ContradictionException;
168
169 /**
170 * Discard the current solution in the optimization problem.
171 *
172 * @throws ContradictionException
173 * if a trivial inconsistency is detected.
174 * @since 2.1
175 */
176 void discardCurrentSolution() throws ContradictionException;
177
178 /**
179 * Allows to check afterwards if the solution provided by the solver is
180 * optimal or not.
181 *
182 * @return
183 */
184 boolean isOptimal();
185 }