/*
* 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.engine.network.activation;
/**
* The Steepened Sigmoid is an activation function typically used with NEAT.
*
* Valid derivative calculated with the R package, so this does work with
* non-NEAT networks too.
*
* It was developed by Ken Stanley while at The University of Texas at Austin.
* http://www.cs.ucf.edu/~kstanley/
*/
public class ActivationSteepenedSigmoid implements ActivationFunction {
/**
* The serial id.
*/
private static final long serialVersionUID = 1L;
/**
* The parameters.
*/
private final double[] params;
/**
* Construct a steepend sigmoid activation function.
*/
public ActivationSteepenedSigmoid() {
this.params = new double[0];
}
/**
* {@inheritDoc}
*/
@Override
public final void activationFunction(final double[] x, final int start,
final int size) {
for (int i = start; i < start + size; i++) {
x[i] = 1.0/(1.0 + Math.exp(-4.9*x[i]));
}
}
/**
* @return The object cloned;
*/
@Override
public final ActivationFunction clone() {
return new ActivationSteepenedSigmoid();
}
/**
* {@inheritDoc}
*/
@Override
public final double derivativeFunction(final double b, final double a) {
double s = Math.exp(-4.9 * a);
return Math.pow(s * 4.9/(1 + s),2);
}
/**
* {@inheritDoc}
*/
@Override
public final String[] getParamNames() {
final String[] result = { };
return result;
}
/**
* {@inheritDoc}
*/
@Override
public final double[] getParams() {
return this.params;
}
/**
* @return Return true, Elliott activation has a derivative.
*/
@Override
public final boolean hasDerivative() {
return true;
}
/**
* {@inheritDoc}
*/
@Override
public final void setParam(final int index, final double value) {
this.params[index] = value;
}
/**
* {@inheritDoc}
*/
@Override
public String getFactoryCode() {
return null;
}
@Override
public String getLabel() {
return "steepenedsigmoid";
}
}