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.specs;
31
32 /**
33 * Represents an optimization problem. The SAT solver will find suboptimal
34 * solutions of the problem until no more solutions are available. The latest
35 * solution found will be the optimal one.
36 *
37 * Such kind of problem is supposed to be handled:
38 *
39 * <pre>
40 * boolean isSatisfiable = false;
41 *
42 * IOptimizationProblem optproblem = (IOptimizationProblem) problem;
43 *
44 * try {
45 * while (optproblem.admitABetterSolution()) {
46 * if (!isSatisfiable) {
47 * if (optproblem.nonOptimalMeansSatisfiable()) {
48 * setExitCode(ExitCode.SATISFIABLE);
49 * if (optproblem.hasNoObjectiveFunction()) {
50 * return;
51 * }
52 * log("SATISFIABLE"); //$NON-NLS-1$
53 * }
54 * isSatisfiable = true;
55 * log("OPTIMIZING..."); //$NON-NLS-1$
56 * }
57 * log("Got one! Elapsed wall clock time (in seconds):" //$NON-NLS-1$
58 * + (System.currentTimeMillis() - getBeginTime()) / 1000.0);
59 * getLogWriter().println(
60 * CURRENT_OPTIMUM_VALUE_PREFIX + optproblem.getObjectiveValue());
61 * optproblem.discardCurrentSolution();
62 * }
63 * if (isSatisfiable) {
64 * setExitCode(ExitCode.OPTIMUM_FOUND);
65 * } else {
66 * setExitCode(ExitCode.UNSATISFIABLE);
67 * }
68 * } catch (ContradictionException ex) {
69 * assert isSatisfiable;
70 * setExitCode(ExitCode.OPTIMUM_FOUND);
71 * }
72 * </pre>
73 *
74 * @author leberre
75 *
76 */
77 public interface IOptimizationProblem extends IProblem {
78
79 /**
80 * Look for a solution of the optimization problem.
81 *
82 * @return true if a better solution than current one can be found.
83 * @throws TimeoutException
84 * if the solver cannot answer in reasonable time.
85 * @see ISolver#setTimeout(int)
86 */
87 boolean admitABetterSolution() throws TimeoutException;
88
89 /**
90 * Look for a solution of the optimization problem when some literals are
91 * satisfied.
92 *
93 * @param assumps
94 * a set of literals in Dimacs format.
95 * @return true if a better solution than current one can be found.
96 * @throws TimeoutException
97 * if the solver cannot answer in reasonable time.
98 * @see ISolver#setTimeout(int)
99 * @since 2.1
100 */
101 boolean admitABetterSolution(IVecInt assumps) throws TimeoutException;
102
103 /**
104 * If the optimization problem has no objective function, then it is a
105 * simple decision problem.
106 *
107 * @return true if the problem is a decision problem, false if the problem
108 * is an optimization problem.
109 */
110 boolean hasNoObjectiveFunction();
111
112 /**
113 * A suboptimal solution has different meaning depending of the optimization
114 * problem considered.
115 *
116 * For instance, in the case of MAXSAT, a suboptimal solution does not mean
117 * that the problem is satisfiable, while in pseudo boolean optimization, it
118 * is true.
119 *
120 * @return true if founding a suboptimal solution means that the problem is
121 * satisfiable.
122 */
123 boolean nonOptimalMeansSatisfiable();
124
125 /**
126 * Compute the value of the objective function for the current solution. A
127 * call to that method only makes sense if hasNoObjectiveFunction()==false.
128 *
129 * DO NOT CALL THAT METHOD THAT WILL BE CALLED AUTOMATICALLY. USE
130 * getObjectiveValue() instead!
131 *
132 * @return the value of the objective function.
133 * @see #getObjectiveValue()
134 */
135 @Deprecated
136 Number calculateObjective();
137
138 /**
139 * Read only access to the value of the objective function for the current
140 * solution.
141 *
142 * @return the value of the objective function for the current solution.
143 * @since 2.1
144 */
145 Number getObjectiveValue();
146
147 /**
148 * Force the value of the objective function.
149 *
150 * This is especially useful to iterate over optimal solutions.
151 *
152 * @throws ContradictionException
153 * @since 2.1
154 */
155 void forceObjectiveValueTo(Number forcedValue)
156 throws ContradictionException;
157
158 /**
159 * Discard the current solution in the optimization problem.
160 *
161 * THE NAME WAS NOT NICE. STILL AVAILABLE TO AVOID BREAKING THE API. PLEASE
162 * USE THE LONGER discardCurrentSolution() instead.
163 *
164 * @throws ContradictionException
165 * if a trivial inconsistency is detected.
166 * @see #discardCurrentSolution()
167 */
168 @Deprecated
169 void discard() throws ContradictionException;
170
171 /**
172 * Discard the current solution in the optimization problem.
173 *
174 * @throws ContradictionException
175 * if a trivial inconsistency is detected.
176 * @since 2.1
177 */
178 void discardCurrentSolution() throws ContradictionException;
179
180 /**
181 * Allows to check afterwards if the solution provided by the solver is
182 * optimal or not.
183 *
184 * @return
185 */
186 boolean isOptimal();
187
188 /**
189 * Allow to set a specific timeout when the solver is in optimization mode.
190 * The solver internal timeout will be set to that value once it has found a
191 * solution. That way, the original timeout of the solver may be reduced if
192 * the solver finds quickly a solution, or increased if the solver finds
193 * regularly new solutions (thus giving more time to the solver each time).
194 *
195 * @since 2.3.3
196 */
197 void setTimeoutForFindingBetterSolution(int seconds);
198 }