TruncationSelection.java

/*
 * Encog(tm) Core v3.4 - Java Version
 * http://www.heatonresearch.com/encog/
 * https://github.com/encog/encog-java-core
 
 * Copyright 2008-2016 Heaton Research, Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 *   
 * For more information on Heaton Research copyrights, licenses 
 * and trademarks visit:
 * http://www.heatonresearch.com/copyright
 */
package org.encog.ml.ea.opp.selection;

import java.io.Serializable;
import java.util.Random;

import org.encog.ml.ea.species.Species;
import org.encog.ml.ea.train.EvolutionaryAlgorithm;

/**
 * Truncation selection chooses a random genome from the top genomes in the
 * population. A percent determines how large this group of top genomes is.
 * 
 * http://en.wikipedia.org/wiki/Truncation_selection
 */
public class TruncationSelection implements SelectionOperator, Serializable {

	/**
	 * The serial id.
	 */
	private static final long serialVersionUID = 1L;

	/**
	 * The trainer.
	 */
	private EvolutionaryAlgorithm trainer;

	/**
	 * The percent to select from.
	 */
	private double percent;

	/**
	 * Construct the truncation selector.
	 * @param theTrainer The trainer.
	 * @param thePercent The top percent to select from.
	 */
	public TruncationSelection(EvolutionaryAlgorithm theTrainer,
			double thePercent) {
		this.trainer = theTrainer;
		this.percent = thePercent;
	}

	/**
	 * {@inheritDoc}
	 */
	@Override
	public int performSelection(Random rnd, Species species) {
		int top = Math.max((int) (species.getMembers().size() * this.percent),
				1);
		int result = rnd.nextInt(top);
		return result;
	}

	/**
	 * {@inheritDoc}
	 */
	@Override
	public int performAntiSelection(Random rnd, Species species) {
		return species.getMembers().size() - performSelection(rnd, species);
	}

	/**
	 * {@inheritDoc}
	 */
	@Override
	public EvolutionaryAlgorithm getTrainer() {
		return this.trainer;
	}

}