/**
* Copyright 2010 Neuroph Project http://neuroph.sourceforge.net
*
* 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.
*/
package org.neuroph.core.transfer;
import java.io.Serializable;
import org.neuroph.util.Properties;
/**
* <pre>
* Gaussian neuron transfer function.
* -(x^2) / (2 * sigma^2)
* f(x) = e
* </pre>
* @author Zoran Sevarac <sevarac@gmail.com>
*/
public class Gaussian extends TransferFunction implements Serializable {
/**
* The class fingerprint that is set to indicate serialization
* compatibility with a previous version of the class.
*/
private static final long serialVersionUID = 1L;
/**
* The sigma parametetar of the gaussian function
*/
private double sigma = 0.5d;
/**
* Creates an instance of Gaussian neuron transfer
*/
public Gaussian() {
}
/**
* Creates an instance of Gaussian neuron transfer function with the
* specified properties.
* @param properties properties of the Gaussian function
*/
public Gaussian(Properties properties) {
try {
this.sigma = (Double)properties.getProperty("transferFunction.sigma");
} catch (NullPointerException e) {
// if properties are not set just leave default values
} catch (NumberFormatException e) {
System.err.println("Invalid transfer function properties! Using default values.");
}
}
@Override
public double getOutput(double net) {
return Math.exp(-0.5d * Math.pow((net / this.sigma), 2d));
}
@Override
public double getDerivative(double net) {
// TODO: check if this is correct
double out = getOutput(net);
double derivative = out * ( -net / (sigma*sigma) );
return derivative;
}
/**
* Returns the sigma parametar of this function
* @return sigma parametar of this function
*/
public double getSigma() {
return this.sigma;
}
/**
* Sets the sigma parametar for this function
* @param sigma value for the slope parametar
*/
public void setSigma(double sigma) {
this.sigma = sigma;
}
}