/*
* 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.operator.features.selection;
import java.util.Random;
import com.rapidminer.operator.features.Population;
/**
* Like RouletteWheel this population operator selects a given fixed number of
* individuals by subdividing a roulette wheel in sections of size proportional
* to the individuals' fitness values. The fitness values are filtered according
* to the Boltzmann theorem.
*
* @author Ingo Mierswa
* @version $Id: BoltzmannSelection.java,v 1.1 2006/04/14 07:47:17 ingomierswa
* Exp $
*/
public class BoltzmannSelection extends RouletteWheel {
private double temperature;
private double delta = 0.0d;
public BoltzmannSelection(int popSize, double temperature, int maxGenerations, boolean dynamic, boolean keepBest, Random random) {
super(popSize, keepBest, random);
this.temperature = temperature;
if (dynamic)
this.delta = this.temperature / (maxGenerations + 1);
}
/**
* Returns a fitness based on the Boltzmann theorem, i.e.
* exp(fitness/temperature). Like for simulated annealing the temperature
* should decrease over time.
*/
public double filterFitness(double fitness) {
return Math.exp(fitness / temperature);
}
/**
* Applies the method from the superclass and decreases the temperature in
* the adaptive case.
*/
public void operate(Population population) {
super.operate(population);
this.temperature -= delta;
}
}