001    package net.sf.cpsolver.ifs.solution;
002    
003    import net.sf.cpsolver.ifs.model.Value;
004    import net.sf.cpsolver.ifs.model.Variable;
005    import net.sf.cpsolver.ifs.util.DataProperties;
006    
007    /**
008     * General implementation of solution comparator for minimal perturbation
009     * problem. <br>
010     * <br>
011     * The solution is better than the best ever found solution when it has more
012     * variables assigned. In the case, when both solutions have the same number of
013     * assigned variables, the one with smaller number of perturbations (i.e.,
014     * variables assigned to non-initial values) is selected. When all solution have
015     * the same number of assigned variables and number of perturbations, better
016     * solution is the one with smaller total value, i.e., the sum of
017     * {@link net.sf.cpsolver.ifs.model.Value#toDouble()} over all assigned
018     * variables.
019     * 
020     * @see Solution
021     * @see net.sf.cpsolver.ifs.solver.Solver
022     * 
023     * @version IFS 1.2 (Iterative Forward Search)<br>
024     *          Copyright (C) 2006 - 2010 Tomas Muller<br>
025     *          <a href="mailto:muller@unitime.org">muller@unitime.org</a><br>
026     *          <a href="http://muller.unitime.org">http://muller.unitime.org</a><br>
027     * <br>
028     *          This library is free software; you can redistribute it and/or modify
029     *          it under the terms of the GNU Lesser General Public License as
030     *          published by the Free Software Foundation; either version 3 of the
031     *          License, or (at your option) any later version. <br>
032     * <br>
033     *          This library is distributed in the hope that it will be useful, but
034     *          WITHOUT ANY WARRANTY; without even the implied warranty of
035     *          MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
036     *          Lesser General Public License for more details. <br>
037     * <br>
038     *          You should have received a copy of the GNU Lesser General Public
039     *          License along with this library; if not see
040     *          <a href='http://www.gnu.org/licenses/'>http://www.gnu.org/licenses/</a>.
041     */
042    public class MPPSolutionComparator<V extends Variable<V, T>, T extends Value<V, T>> implements SolutionComparator<V, T> {
043    
044        public MPPSolutionComparator() {
045        }
046    
047        /** No parameters are used so far. */
048        public MPPSolutionComparator(DataProperties properties) {
049        }
050    
051        @Override
052        public boolean isBetterThanBestSolution(Solution<V, T> currentSolution) {
053            if (currentSolution.getBestInfo() == null)
054                return true;
055            int unassigned = currentSolution.getModel().nrUnassignedVariables();
056            if (currentSolution.getModel().getBestUnassignedVariables() != unassigned)
057                return currentSolution.getModel().getBestUnassignedVariables() > unassigned;
058            int pert = currentSolution.getModel().perturbVariables().size();
059            if (currentSolution.getModel().getBestPerturbations() != pert)
060                return currentSolution.getModel().getBestPerturbations() > pert;
061            return currentSolution.getModel().getTotalValue() < currentSolution.getBestValue();
062        }
063    
064    }