/*
* Kodkod -- Copyright (c) 2005-2007, Emina Torlak
*
* Permission is hereby granted, free of charge, to any person obtaining a copy
* of this software and associated documentation files (the "Software"), to deal
* in the Software without restriction, including without limitation the rights
* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
* copies of the Software, and to permit persons to whom the Software is
* furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice shall be included in
* all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
* THE SOFTWARE.
*/
package kodkod.engine.ucore;
import kodkod.engine.satlab.ReductionStrategy;
import kodkod.engine.satlab.ResolutionTrace;
import kodkod.util.ints.IntSet;
import kodkod.util.ints.Ints;
/**
* A non-optimal minimization strategy based on the Empty Clause Cone algorithm.
* @author Emina Torlak
* @see <a href="http://research.microsoft.com/users/lintaoz/papers/SAT_2003_core.pdf">L. Zhang and S. Malik. <i>Extracting small unsatisfiable cores from unsatisfiable
* Boolean formula.</i> In Proceedings of Sixth International Conference on Theory and Applications of
* Satisfiability Testing (SAT '03). 2003.</a>
*/
public final class ECFPStrategy implements ReductionStrategy {
private int lastCore;
/**
* Constructs a new instance of the empty clause cone strategy for
* minimizing unsatisfiable cores.
*/
public ECFPStrategy() {
lastCore = Integer.MAX_VALUE;
}
/**
* {@inheritDoc}
* @see kodkod.engine.satlab.ReductionStrategy#next(kodkod.engine.satlab.ResolutionTrace)
*/
public IntSet next(final ResolutionTrace trace) {
final IntSet core = trace.core();
if (lastCore > core.size()) {
lastCore = core.size();
return core;
} else {
lastCore = Integer.MIN_VALUE;
return Ints.EMPTY_SET;
}
}
}