OperationList.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;

import java.util.Random;

import org.encog.util.obj.ChooseObject;
import org.encog.util.obj.ObjectHolder;

/**
 * This class holds a list of evolutionary operators. Each operator is given a
 * probability weight. Based on the number of parents available a random
 * selection of an operator can be made based on the probability given each of
 * the operators.
 */
public class OperationList extends ChooseObject<EvolutionaryOperator> {

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

	/**
	 * Determine the maximum number of offspring that might be produced by any
	 * of the operators in this list.
	 * 
	 * @return The maximum number of offspring.
	 */
	public int maxOffspring() {
		int result = 0;
		for (final ObjectHolder<EvolutionaryOperator> holder : getList()) {
			result = Math.max(result, holder.getObj().offspringProduced());
		}
		return result;
	}

	/**
	 * Determine the maximum number of parents required by any of the operators
	 * in the list.
	 * 
	 * @return The maximum number of parents.
	 */
	public int maxParents() {
		int result = Integer.MIN_VALUE;
		for (final ObjectHolder<EvolutionaryOperator> holder : getList()) {
			result = Math.max(result, holder.getObj().parentsNeeded());
		}
		return result;
	}

	/**
	 * Pick a operator based on the number of parents available.
	 * 
	 * @param rnd
	 *            A random number generator.
	 * @param maxParents
	 *            The maximum number of parents available.
	 * @return The operator that was selected.
	 */
	public EvolutionaryOperator pickMaxParents(final Random rnd,
			final int maxParents) {

		// determine the total probability of eligible operators
		double total = 0;
		for (final ObjectHolder<EvolutionaryOperator> holder : getList()) {
			if (holder.getObj().parentsNeeded() <= maxParents) {
				total += holder.getProbability();
			}
		}

		// choose an operator
		final double r = rnd.nextDouble() * total;
		double current = 0;
		for (final ObjectHolder<EvolutionaryOperator> holder : getList()) {
			if (holder.getObj().parentsNeeded() <= maxParents) {
				current += holder.getProbability();
				if (r < current) {
					return holder.getObj();
				}
			}
		}

		return null;
	}

}