bulkfitnessoffsetremover.java

用java语言写的遗传算法库

/*
 * This file is part of JGAP.
 *
 * JGAP offers a dual license model containing the LGPL as well as the MPL.
 *
 * For licencing information please see the file license.txt included with JGAP
 * or have a look at the top of class org.jgap.Chromosome which representatively
 * includes the JGAP license policy applicable for any file delivered with JGAP.
 */
package org.jgap.impl;

import java.util.*;
import org.jgap.*;

/**
 * <p>
 * Takes away the fitness offset of the population to evolve.
 * The fitness function values of the population of {@link org.jgap.Chromosome}
 * instances will start from a minimum of 1 afterwards.
 * </p>
 * <p>
 * The removal of an offset in the fitness values of a population strengthens the
 * "survival of the fittest" effect of a selector that performs selection
 * upon fitness values. A high offset in the fitness values of a population
 * lowers the relative difference between the fitness values of the Chromosomes in
 * a population.
 * </p>
 * <h3>Example of applicability</h3>
 * <p>
 * You are optimizing a black box with <i>n</i> parameters that are mapped
 * to {@link org.jgap.Chromosome} instances each having <i>n</i> {@link org.jgap.Gene}
 * instances.<br>
 * You want to minimize the answer time of the black box and provide
 * a {@link org.jgap.FitnessFunction#evaluate(org.jgap.Chromosome)}
 * that takes the genes out of the chromosome, put's it's {@link org.jgap.Gene#getAllele()}
 * values to the parameters and measures the answer time of the black box
 * (by invoking it's service to optimize). <br>
 * The longer the time takes, the worse it's fitness is, so you have to
 * invert the measured times to fitness values:
 * <a name="bboptimizer"/>
 * <pre>
 * <font color="#0011EE">
 * class BlackBoxOptimizer extends org.jgap.FitnessFunction{
 *   private BlackBox bbox;
 *   <font color="#999999">//Additional code: constructors</font>
 *   <font color="#999999">...</font>
 *   public double evaluate(org.jgap.Chromosome chromosome){
 *     double fitness = 0;
 *     <font color="#999999">// get the Gene[] & put the parameters into the box.
 *     ...
 *     </font>
 *     long duration = System.currentTimeMillis();  <font color="#999999">// You certainly will use an advanced StopWatch...</font>
 *     this.bbox.service();  <font color="#999999">// The black boxes service to optimize.</font>
 *     duration = System.currentTimeMillis()-duration;
 *     <font color="#999999">// transform the time into fitness value:</font>
 *     fitness = double.MAX_VALUE - (double)duration;
 *     return fitness;
 *   }
 * }
 * </font>
 * </pre>
 * </p>
 * <p>
 * <h4>We might get the following results (each row stands for a Chromosome, the table is a population):</h4>
 * <table border="1">
 * <tr align="left" valign="top">
 * <th>
 * duration
 * </th>
 * <th>
 * fitness
 * </th>
 * <th>
 * piece of fitness cake
 * </th>
 * </tr>
 * <tr align="left" valign="top">
 * <td>
 * 2000
 * </td>
 * <td>
 * 9218868437227403311
 * </td>
 * <td>
 * 33.333333333333336949106088992532 %
 * </td>
 * </tr>
 * <tr align="left" valign="top">
 * <td>
 * 3000
 * </td>
 * <td>
 * 9218868437227402311
 * </td>
 * <td>
 * 33.333333333333333333333333333333 %
 * </td>
 * </tr>
 * <tr align="left" valign="top">
 * <td>
 * 4000
 * </td>
 * <td>
 * 9218868437227401311
 * </td>
 * <td>
 * 33.333333333333329717560577674135 %
 * </td>
 * </tr>
 * </table>
 * </p>
 * <p>
 * If any {@link org.jgap.NaturalSelector} performs selection based upon the fitness values, it
 * will have to put those values in relation to each other. As a fact, the probability
 * to select the Chromosome that contained the black box parameters that caused an answer time
 * of 4000 ms is "equal" to the probability to select the Chromosome that caused a black box
 * answer time to be 2000 ms!
 * </p>
 * <p>
 * Of course one could work around that problem by replacing the <tt>Integer.MAX_VALUE</tt>
 * transformation by a fixed maximum value the black box would need for the service.
 * But what, if you have no guaranteed maximum answer time for the service of the black box ?
 * Even if you have got one, it will be chosen sufficently high above the average answer
 * time thus letting your fitness function return values with a high offset in the fitness.
 * </p>
 * <p>
 * <h4>This is, what happens, if you use this instance for fitness evaluation:</h4>
 * <table border="1">
 * <tr align="left" valign="top">
 * <th>
 * duration
 * </th>
 * <th>
 * fitness
 * </th>
 * <th>
 * piece of fitness cake
 * </th>
 * </tr>
 * <tr align="left" valign="top">
 * <td>
 * 2000
 * </td>
 * <td>
 * 2001
 * </td>
 * <td>
 * 66.63 %
 * </td>
 * </tr>
 * <tr align="left" valign="top">
 * <td>
 * 3000
 * </td>
 * <td>
 * 1001
 * </td>
 * <td>
 * 33.33 %
 * </td>
 * </tr>
 * <tr align="left" valign="top">
 * <td>
 * 4000
 * </td>
 * <td>
 * 1
 * </td>
 * <td>
 * 0.03 %
 * </td>
 * </tr>
 * </table>
 * </p>
 * <h3>Example of usage</h3>
 *
 * <p>
 * This example shows how to use this instance for cutting fitness offsets.
 * It is the same example as used <a href="#bboptimizer">above</a>.
 * <pre>
 * <font color="#0011EE">
 * class BlackBoxOptimizer extends org.jgap.FitnessFunction{
 *   <font color="#999999">// Additional code: constructors
 *   ...</font>
 *   public double evaluate(org.jgap.Chromosome chromosome){
 *     <font color="#999999">.... // As shown above.</font>
 *   }
 *
 *   public void startOptimization(org.jgap.Configuration gaConf)throws InvalidConfigurationException{
 *     <font color="#999999">// The given Configuration may be preconfigured with
 *     // NaturalSelector & GeneticOperator instances,.
 *     // But should not contain a FitnessFunction or BulkFitnessFunction!</font>
 *     <b>gaConf.setBulkFitnessFunction(new BulkFitnessOffsetRemover(this));</b>
 *     <font color="#999999">// Why does it work? We implement FitnessFunction!
 *     // Still to do here:
 *     // - Create a sample chromosome according to your blackbox & set it to the configuration.
 *     // - Create a random inital Genotype.
 *     // - loop over a desired amount of generations invoking aGenotype.evolve()..</font>
 *   }
 * }
 * </font>
 * </pre>
 * </p>
 * @author Achim Westermann
 * @since 2.2
 *
 */
public class BulkFitnessOffsetRemover
    extends BulkFitnessFunction {
  /** String containing the CVS revision. Read out via reflection!*/
  private final static String CVS_REVISION = "$Revision: 1.3 $";

  /*
   * Replace this member by the Configuration as
   * Replace this member by the Configuration as
   * soon as Configuration allows bulk fitness function and
   * fitness function to be stored both in it.
   */
  private FitnessFunction ff;