/*
* 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 step activation function is a very simple activation function. It is the
* activation function that was used by the original perceptron. Using the
* default parameters it will return 1 if the input is 0 or greater. Otherwise
* it will return 1.
*
* The center, low and high properties allow you to define how this activation
* function works. If the input is equal to center or higher the high property
* value will be returned, otherwise the low property will be returned. This
* activation function does not have a derivative, and can not be used with
* propagation training, or any other training that requires a derivative.
*
*/
public class ActivationStep implements ActivationFunction {
/**
* The step center parameter.
*/
public static final int PARAM_STEP_CENTER = 0;
/**
* The step low parameter.
*/
public static final int PARAM_STEP_LOW = 1;
/**
* The step high parameter.
*/
public static final int PARAM_STEP_HIGH = 2;
/**
* The serial ID.
*/
private static final long serialVersionUID = 3416782010146745754L;
/**
* The parameters.
*/
private double[] params;
/**
* Construct a step activation function.
*
* @param low
* The low of the function.
* @param center
* The center of the function.
* @param high
* The high of the function.
*/
public ActivationStep(final double low, final double center,
final double high) {
this.params = new double[3];
this.params[ActivationStep.PARAM_STEP_CENTER] = center;
this.params[ActivationStep.PARAM_STEP_LOW] = low;
this.params[ActivationStep.PARAM_STEP_HIGH] = high;
}
/**
* Create a basic step activation with low=0, center=0, high=1.
*/
public ActivationStep() {
this(0.0, 0.0, 1.0);
}
/**
* @return The center.
*/
public double getCenter() {
return this.params[ActivationStep.PARAM_STEP_CENTER];
}
/**
* @return The low value.
*/
public double getLow() {
return this.params[ActivationStep.PARAM_STEP_LOW];
}
/**
* @return The high value.
*/
public double getHigh() {
return this.params[ActivationStep.PARAM_STEP_HIGH];
}
/**
* @return A clone of this object.
*/
@Override
public ActivationFunction clone() {
ActivationStep result = new ActivationStep(getLow(), getCenter(),
getHigh());
return result;
}
/**
* @return Returns true, this activation function has a derivative.
*/
public boolean hasDerivative() {
return true;
}
/**
* Set the center of this function.
*
* @param d
* The center of this function.
*/
public void setCenter(final double d) {
this.setParam(ActivationStep.PARAM_STEP_CENTER, d);
}
/**
* Set the high of this function.
*
* @param d
* The high of this function.
*/
public void setHigh(final double d) {
this.setParam(ActivationStep.PARAM_STEP_HIGH, d);
}
/**
* Set the low of this function.
*
* @param d
* The low of this function.
*/
public void setLow(final double d) {
this.setParam(ActivationStep.PARAM_STEP_LOW, d);
}
/**
* {@inheritDoc}
*/
@Override
public void activationFunction(final double[] x, final int start,
final int size) {
for (int i = start; i < start + size; i++) {
if (x[i] >= params[ActivationStep.PARAM_STEP_CENTER]) {
x[i] = params[ActivationStep.PARAM_STEP_HIGH];
} else {
x[i] = params[ActivationStep.PARAM_STEP_LOW];
}
}
}
/**
* {@inheritDoc}
*/
@Override
public double derivativeFunction(final double d) {
return 1.0;
}
/**
* {@inheritDoc}
*/
@Override
public String[] getParamNames() {
final String[] result = { "center", "low", "high" };
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) {
return null;
}
}