/*
* Encog(tm) Core v2.5 - Java Version
* http://www.heatonresearch.com/encog/
* http://code.google.com/p/encog-java/
* Copyright 2008-2010 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.examples.neural.activation;
import org.encog.engine.network.activation.ActivationFunction;
import org.encog.engine.util.BoundMath;
/**
* The sigmoid activation function takes on a sigmoidal shape. Only positive
* numbers are generated. Do not use this activation function if negative number
* output is desired.
*/
public class ActivationSigmoidPosNeg implements ActivationFunction {
/**
* The offset to the parameter that holds the sigmoid slope.
*/
public static final int PARAM_SIGMOID_POS_NEG_SLOPE = 0;
/**
* Serial id for this class.
*/
private static final long serialVersionUID = 5622349801036468572L;
/**
* The parameters.
*/
private double[] params;
/**
* Construct a basic sigmoid function, with a slope of 1.
*/
public ActivationSigmoidPosNeg() {
this.params = new double[1];
this.params[ActivationSigmoidPosNeg.PARAM_SIGMOID_POS_NEG_SLOPE] = 1;
}
/**
* @return The object cloned;
*/
@Override
public ActivationFunction clone() {
return new ActivationSigmoidPosNeg();
}
/**
* @return Get the slope of the activation function.
*/
public double getSlope() {
return this.params[ActivationSigmoidPosNeg.PARAM_SIGMOID_POS_NEG_SLOPE];
}
/**
* @return True, sigmoid has a derivative.
*/
@Override
public boolean hasDerivative() {
return true;
}
/**
* {@inheritDoc}
*/
@Override
public void activationFunction(final double[] x, final int start,
final int size) {
for (int i = start; i < start + size; i++) {
x[i] = 2.0*(1.0 / (1.0 + BoundMath.exp(-params[0] * x[i])))-1.0;
}
}
/**
* {@inheritDoc}
*/
@Override
public double derivativeFunction(final double x) {
return Math.pow( params[0] * x * (1.0 - x),2);
}
/**
* {@inheritDoc}
*/
@Override
public String[] getParamNames() {
final String[] results = { "slope" };
return results;
}
/**
* {@inheritDoc}
*/
@Override
public double[] getParams() {
// TODO Auto-generated method stub
return this.params;
}
/**
* {@inheritDoc}
*/
@Override
public void setParam(final int index, final double value) {
this.params[index] = value;
}
/**
* {@inheritDoc}
*/
@Override
public String getOpenCLExpression(final boolean derivative) {
if (derivative) {
return "(1.0f / (1.0f + exp(-slope * x)))";
} else {
return "(slope * x * (1.0f - x))";
}
}
}