/*
 *  RapidMiner
 *
 *  Copyright (C) 2001-2008 by Rapid-I and the contributors
 *
 *  Complete list of developers available at our web site:
 *
 *       http://rapid-i.com
 *
 *  This program is free software: you can redistribute it and/or modify
 *  it under the terms of the GNU Affero General Public License as published by
 *  the Free Software Foundation, either version 3 of the License, or
 *  (at your option) any later version.
 *
 *  This program 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 Affero General Public License for more details.
 *
 *  You should have received a copy of the GNU Affero General Public License
 *  along with this program.  If not, see http://www.gnu.org/licenses/.
 */
package com.rapidminer.tools.math.optimization.ec.es;

import java.util.Iterator;
import java.util.LinkedList;

import com.rapidminer.tools.LoggingHandler;


/**
 * Implements the 1/5-Rule for dynamic parameter adaption of the variance of a
 * {@link GaussianMutation}. The interval size should have the same size as the
 * changable components, i.e. the number of examples (alphas).
 * 
 * @author Ingo Mierswa
 * @version $Id: VarianceAdaption.java,v 1.3 2008/05/09 19:23:16 ingomierswa Exp $
 */
public class VarianceAdaption implements PopulationOperator {

	/**
	 * Waits this number of intervals before variance adaption is applied.
	 * Usually 10.
	 */
	private static final int WAIT_INTERVALS = 2;

	/** Used factor for shrinking and enlarging. Usually 0.85. */
	private static final double FACTOR = 0.85;

	/** The mutation. */
	private GaussianMutation mutation = null;

	/** The interval size in which the new variance is calculated. */
	private int intervalSize;

	/** Remember for all positions if an improval was found. */
	private LinkedList<Boolean> successList = new LinkedList<Boolean>();

    /** The logging handler. */
    private LoggingHandler logging;
    
	/**
	 * The interval size should be as big as the changeable components, i.e. the
	 * number of examples (alphas).
	 */
	public VarianceAdaption(GaussianMutation mutation, int intervalSize, LoggingHandler logging) {
		this.mutation = mutation;
		this.intervalSize = intervalSize;
        this.logging = logging;
	}

	public void operate(Population population) {
		if (population.getGenerationsWithoutImprovement() < 2) {
			successList.add(true);
		} else {
			successList.add(false);
		}

		if (population.getGeneration() >= WAIT_INTERVALS * intervalSize) {
			successList.removeFirst();
			if ((population.getGeneration() % intervalSize) == 0) {
				int successCount = 0;
				Iterator<Boolean> i = successList.iterator();
				while (i.hasNext())
					if (i.next())
						successCount++;

				if (((double) successCount / (double) (WAIT_INTERVALS * intervalSize)) < 0.2) {
                    double[] sigma = mutation.getSigma();
                    for (int s = 0; s < sigma.length; s++) {
                        sigma[s] *= FACTOR;
                    }
					mutation.setSigma(sigma);
					logging.log("Applying 1/5-rule: shrink variance!");
				} else {
                    double[] sigma = mutation.getSigma();
                    for (int s = 0; s < sigma.length; s++) {
                        sigma[s] /= FACTOR;
                    }
                    mutation.setSigma(sigma);
					logging.log("Applying 1/5-rule: enlarge variance!");
				}
			}
		}
	}
}