/*
 * Copyright 2007-2013
 * Licensed under GNU Lesser General Public License
 * 
 * This file is part of EpochX
 * 
 * EpochX 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.
 * 
 * EpochX 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 EpochX. If not, see <http://www.gnu.org/licenses/>.
 * 
 * The latest version is available from: http://www.epochx.org
 */

package org.epochx.fitness.stat;

import org.epochx.Population;
import org.epochx.event.GenerationEvent.EndGeneration;
import org.epochx.event.stat.AbstractStat;
import org.epochx.fitness.DoubleFitness;

/**
 * Stat that provides the average fitness error of the population at the end of a
 * generation. This stat can only be used with <code>DoubleFitness</code>.
 * 
 * @see DoubleFitness
 */
public class GenerationAverageDoubleFitnessError extends AbstractStat<EndGeneration> {

	/**
	 * The average fitness error.
	 */
	private double error;

	/**
	 * Constructs a <code>GenerationAverageDoubleFitnessError</code>.
	 */
	public GenerationAverageDoubleFitnessError() {
		super(GenerationStandardDeviationDoubleFitness.class);
	}

	/**
	 * Computes the average fitness error of the population.
	 * 
	 * @param event the <code>EndGeneration</code> event object.
	 */
	@Override
	public void refresh(EndGeneration event) {
		double stdev = AbstractStat.get(GenerationStandardDeviationDoubleFitness.class).getStandardDeviation();
		Population population = event.getPopulation();
		
		error = stdev / Math.sqrt(population.size());
	}

	/**
	 * Returns the average fitness error.
	 * 
	 * @return the average fitness error.
	 */
	public double getError() {
		return error;
	}

	/**
	 * Returns a string representation of the average fitness error.
	 * 
	 * @return a string representation of the average fitness error.
	 */
	@Override
	public String toString() {
		return Double.toString(error);
	}
}