/*
* 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.engine.network.activation;
/**
* The Linear layer is really not an activation function at all. The input is
* simply passed on, unmodified, to the output. This activation function is
* primarily theoretical and of little actual use. Usually an activation
* function that scales between 0 and 1 or -1 and 1 should be used.
*/
public class ActivationLinear implements ActivationFunction {
/**
* The offset to the parameter that holds the linear slope.
*/
public static final int PARAM_LINEAR_SLOPE = 0;
/**
* Serial id for this class.
*/
private static final long serialVersionUID = -5356580554235104944L;
/**
* The parameters.
*/
private double[] params;
/**
* Construct a linear activation function, with a slope of 1.
*/
public ActivationLinear() {
this.params = new double[1];
this.params[ActivationLinear.PARAM_LINEAR_SLOPE] = 1;
}
/**
* @return The object cloned.
*/
@Override
public ActivationFunction clone() {
return new ActivationLinear();
}
/**
* @return Return true, linear has a 1 derivative.
*/
public boolean hasDerivative() {
return true;
}
/**
* @return The slope of the activation function.
*/
public double getSlope() {
return this.params[ActivationLinear.PARAM_LINEAR_SLOPE];
}
/**
* {@inheritDoc}
*/
@Override
public void activationFunction(final double[] x, final int start,
final int size) {
for (int i = start; i < start + size; i++) {
x[i] = x[i] * params[0];
}
}
/**
* {@inheritDoc}
*/
@Override
public double derivativeFunction(final double d) {
return 1;
}
/**
* {@inheritDoc}
*/
@Override
public String[] getParamNames() {
final String[] result = { };
return result;
}
/**
* {@inheritDoc}
*/
@Override
public double[] getParams() {
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 "(1.0)";
} else {
return "(x)";
}
}
}