/*
* 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 bipolar sigmoid activation function is like the regular sigmoid activation function,
* except Bipolar sigmoid activation function. TheOutput range is -1 to 1 instead of the more normal 0 to 1.
*
* This activation is typically part of a CPPN neural network, such as
* HyperNEAT.
*
* The idea for this activation function was developed by Ken Stanley, of
* the University of Texas at Austin.
* http://www.cs.ucf.edu/~kstanley/
*/
public class ActivationBipolarSteepenedSigmoid implements ActivationFunction {
/**
* The serial id.
*/
private static final long serialVersionUID = 1L;
/**
* {@inheritDoc}
*/
@Override
public void activationFunction(double[] d, int start, int size) {
for(int i=start;i<start+size;i++) {
d[i] = (2.0 / (1.0 + Math.exp(-4.9 * d[i]))) - 1.0;
}
}
/**
* {@inheritDoc}
*/
@Override
public double derivativeFunction(double b, double a) {
return 1;
}
/**
* {@inheritDoc}
*/
@Override
public boolean hasDerivative() {
return true;
}
/**
* {@inheritDoc}
*/
@Override
public double[] getParams() {
return ActivationLinear.P;
}
/**
* {@inheritDoc}
*/
@Override
public void setParam(int index, double value) {
}
/**
* {@inheritDoc}
*/
@Override
public String[] getParamNames() {
return ActivationLinear.N;
}
/**
* {@inheritDoc}
*/
@Override
public final ActivationFunction clone() {
return new ActivationBipolarSteepenedSigmoid();
}
/**
* {@inheritDoc}
*/
@Override
public String getFactoryCode() {
return null;
}
@Override
public String getLabel() {
return "bipolar-steepenedsigmoid";
}
}