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The constraint solver library contains a local search based framework that allows modeling of a problem using constraint programming primitives (variables, values, constraints).
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package org.cpsolver.exam.criteria;

import java.util.Collection;
import java.util.Set;

import org.cpsolver.exam.criteria.additional.PeriodViolation;
import org.cpsolver.exam.model.Exam;
import org.cpsolver.exam.model.ExamPeriodPlacement;
import org.cpsolver.exam.model.ExamPlacement;
import org.cpsolver.ifs.assignment.Assignment;
import org.cpsolver.ifs.solver.Solver;
import org.cpsolver.ifs.util.DataProperties;


/**
 * Cost for using a period. See {@link ExamPeriodPlacement#getPenalty()} for more details.
 * 


 * A weight for period penalty can be set by problem property
 * Exams.PeriodWeight, or in the input xml file, property periodWeight.
 * 
 * 

 * 
 * @author  Tomas Muller
 * @version ExamTT 1.3 (Examination Timetabling)

 *          Copyright (C) 2008 - 2014 Tomas Muller

 *          [email protected]

 *          http://muller.unitime.org

 * 

 *          This library is free software; you can redistribute it and/or modify
 *          it under the terms of the GNU Lesser General Public License as
 *          published by the Free Software Foundation; either version 3 of the
 *          License, or (at your option) any later version. 

 * 

 *          This library is distributed in the hope that it will be useful, but
 *          WITHOUT ANY WARRANTY; without even the implied warranty of
 *          MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
 *          Lesser General Public License for more details. 

 * 

 *          You should have received a copy of the GNU Lesser General Public
 *          License along with this library; if not see
 *          http://www.gnu.org/licenses/.
 */
public class PeriodPenalty extends ExamCriterion {
    protected Integer iSoftPeriods = null;
    
    @Override
    public boolean init(Solver solver) {
        if (super.init(solver)) {
            iSoftPeriods = solver.getProperties().getPropertyInteger("Exam.SoftPeriods", null);
            if (iSoftPeriods != null) {
                PeriodViolation pv = new PeriodViolation();
                getModel().addCriterion(pv);
                return pv.init(solver);
            }
        }
        return true;
    }
    
    @Override
    public String getWeightName() {
        return "Exams.PeriodWeight";
    }
    
    @Override
    public String getXmlWeightName() {
        return "periodWeight";
    }
    
    @Override
    public double getWeightDefault(DataProperties config) {
        return 1.0;
    }
    
    @Override
    public double getValue(Assignment assignment, ExamPlacement value, Set conflicts) {
        return (iSoftPeriods == null || (value.getPeriodPlacement().getExamPenalty() != iSoftPeriods &&  value.getPeriodPlacement().getPeriod().getPenalty() != iSoftPeriods) ? value.getPeriodPlacement().getPenalty() : 0.0);
    }

    @Override
    public double[] getBounds(Assignment assignment, Collection variables) {
        double[] bounds = new double[] { 0.0, 0.0 };
        for (Exam exam : variables) {
            if (!exam.getPeriodPlacements().isEmpty()) {
                int minPenalty = Integer.MAX_VALUE, maxPenalty = Integer.MIN_VALUE;
                for (ExamPeriodPlacement periodPlacement : exam.getPeriodPlacements()) {
                    if (iSoftPeriods != null && (periodPlacement.getExamPenalty() == iSoftPeriods || periodPlacement.getPeriod().getPenalty() == iSoftPeriods)) continue;
                    minPenalty = Math.min(minPenalty, periodPlacement.getPenalty());
                    maxPenalty = Math.max(maxPenalty, periodPlacement.getPenalty());
                }
                bounds[0] += minPenalty;
                bounds[1] += maxPenalty;
            }
        }
        return bounds;
    }
    
    @Override
    public String toString(Assignment assignment) {
        return "PP:" + sDoubleFormat.format(getValue(assignment));
    }
}