/*******************************************************************************
* Copyright (C) 2013 Stefan Schroeder
*
* 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 3.0 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/>.
******************************************************************************/
package jsprit.core.algorithm.termination;
import jsprit.core.algorithm.SearchStrategy.DiscoveredSolution;
import jsprit.core.algorithm.VehicleRoutingAlgorithm;
import jsprit.core.algorithm.listener.AlgorithmStartsListener;
import jsprit.core.algorithm.listener.IterationEndsListener;
import jsprit.core.algorithm.listener.IterationStartsListener;
import jsprit.core.problem.VehicleRoutingProblem;
import jsprit.core.problem.solution.VehicleRoutingProblemSolution;
import jsprit.core.util.Solutions;
import org.apache.commons.math.stat.StatUtils;
import org.apache.commons.math.stat.descriptive.moment.StandardDeviation;
import org.apache.logging.log4j.LogManager;
import org.apache.logging.log4j.Logger;
import java.util.Collection;
/**
* Terminates algorithm prematurely based on variationCoefficient (http://en.wikipedia.org/wiki/Coefficient_of_variation).
*
* <p>Note, that this must be registered as AlgorithmListener <br>
* It will be activated by:<br>
*
* <code>algorithm.setPrematureAlgorithmTermination(this);</code><br>
* <code>algorithm.addListener(this);</code>
*
*
* @author stefan schroeder
*
*/
public class VariationCoefficientTermination implements PrematureAlgorithmTermination, IterationStartsListener, AlgorithmStartsListener, IterationEndsListener{
private final static Logger logger = LogManager.getLogger(VariationCoefficientTermination.class);
private final int noIterations;
private final double variationCoefficientThreshold;
private int currentIteration;
private double[] solutionValues;
private VehicleRoutingProblemSolution lastAccepted = null;
/**
* Constructs termination.
*
* @param noIterations size of the sample, i.e. number previous solutions values to take into account. If for example
* noIterations = 10 then every 10th iteration the variationCoefficient will be calculated with the
* last 10 solution values.
* @param variationCoefficientThreshold the threshold used to terminate the algorithm. If the calculated variationCoefficient
* is smaller than the specified threshold, the algorithm terminates.
*/
public VariationCoefficientTermination(int noIterations, double variationCoefficientThreshold) {
super();
this.noIterations = noIterations;
this.variationCoefficientThreshold = variationCoefficientThreshold;
solutionValues = new double[noIterations];
logger.info("initialise " + this);
}
@Override
public String toString() {
return "[name=VariationCoefficientBreaker][variationCoefficientThreshold="+variationCoefficientThreshold+"][iterations="+ noIterations +"]";
}
@Override
public boolean isPrematureBreak(DiscoveredSolution discoveredSolution) {
if(discoveredSolution.isAccepted()){
lastAccepted = discoveredSolution.getSolution();
solutionValues[currentIteration] = discoveredSolution.getSolution().getCost();
}
else{
if(lastAccepted != null){
solutionValues[currentIteration] = lastAccepted.getCost();
}
else solutionValues[currentIteration] = Integer.MAX_VALUE;
}
if(currentIteration == (noIterations - 1)){
double mean = StatUtils.mean(solutionValues);
double stdDev = new StandardDeviation(true).evaluate(solutionValues, mean);
double variationCoefficient = stdDev / mean;
if(variationCoefficient < variationCoefficientThreshold){
return true;
}
}
return false;
}
private void reset(){
currentIteration = 0;
}
@Override
public void informAlgorithmStarts(VehicleRoutingProblem problem,VehicleRoutingAlgorithm algorithm,Collection<VehicleRoutingProblemSolution> solutions) {
reset();
}
@Override
public void informIterationEnds(int i, VehicleRoutingProblem problem, Collection<VehicleRoutingProblemSolution> solutions) {
if(currentIteration == (noIterations - 1)){
reset();
}
else{
currentIteration++;
}
}
@Override
public void informIterationStarts(int i, VehicleRoutingProblem problem, Collection<VehicleRoutingProblemSolution> solutions) {
if(lastAccepted == null) lastAccepted = Solutions.bestOf(solutions);
}
}