/* * Encog Neural Network and Bot Library for Java v1.x * http://www.heatonresearch.com/encog/ * http://code.google.com/p/encog-java/ *  * Copyright 2008, Heaton Research Inc., and individual contributors. * See the copyright.txt in the distribution for a full listing of  * individual contributors. * * This is free software; you can redistribute it and/or modify it * under the terms of the GNU Lesser General Public License as * published by the Free Software Foundation; either version 2.1 of * the License, or (at your option) any later version. * * This software 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 * Lesser General Public License for more details. * * You should have received a copy of the GNU Lesser General Public * License along with this software; if not, write to the Free * Software Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA * 02110-1301 USA, or see the FSF site: http://www.fsf.org. */package org.encog.neural.activation;import java.io.Serializable;import org.encog.neural.persist.EncogPersistedObject;/** * ActivationFunction: This interface allows various activation functions to be * used with the neural network. Activation functions are applied to * the output from each layer of a neural network. Activation functions scale * the output into the desired range. *  * Methods are provided both to process the activation function, as well as * the derivative of the function.  Some training algorithms, particularly * back propagation, require that it be possible to take the derivative * of the activation function. *  * Not all activation functions support derivatives.  If you implement an  * activation function that is not derivable then an exception should be thrown * inside of the derivativeFunction method implementation. *  * Non-derivable activation functions are perfectly valid, they simply cannot be * used with every training algorithm.  */public interface ActivationFunction extends Serializable, EncogPersistedObject {	/**	 * A activation function for a neural network.	 * 	 * @param d	 *            The input to the function.	 * @return The output from the function.	 */	double activationFunction(double d);	/**	 * Performs the derivative of the activation function function on the input.	 * 	 * @param d	 *            The input.	 * @return The output.	 */	double derivativeFunction(double d);}