org.encog.engine.network.activation
Class ActivationStep

java.lang.Object
  org.encog.engine.network.activation.ActivationStep

All Implemented Interfaces:

Serializable, Cloneable, ActivationFunction

public class ActivationStep
extends Object
implements ActivationFunction

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.

See Also:

Serialized Form

Field Summary

static int	PARAM_STEP_CENTER The step center parameter.
static int	PARAM_STEP_HIGH The step high parameter.
static int	PARAM_STEP_LOW The step low parameter.

Constructor Summary

ActivationStep()
Create a basic step activation with low=0, center=0, high=1.

ActivationStep(double low, double center, double high)
Construct a step activation function.

Method Summary

void	activationFunction(double[] x, int start, int size) Implements the activation function.
ActivationFunction	clone()
double	derivativeFunction(double b, double a) Calculate the derivative.
double	getCenter()
String	getFactoryCode()
double	getHigh()
double	getLow()
String[]	getParamNames()
double[]	getParams()
boolean	hasDerivative()
void	setCenter(double d) Set the center of this function.
void	setHigh(double d) Set the high of this function.
void	setLow(double d) Set the low of this function.
void	setParam(int index, double value) Set one of the params for this activation function.

Methods inherited from class java.lang.Object

equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

PARAM_STEP_CENTER

public static final int PARAM_STEP_CENTER

The step center parameter.

See Also:

Constant Field Values

PARAM_STEP_LOW

public static final int PARAM_STEP_LOW

The step low parameter.

See Also:

Constant Field Values

PARAM_STEP_HIGH

public static final int PARAM_STEP_HIGH

The step high parameter.

See Also:

Constant Field Values

Constructor Detail

ActivationStep

public ActivationStep()

Create a basic step activation with low=0, center=0, high=1.

ActivationStep

public ActivationStep(double low,
                      double center,
                      double high)

Construct a step activation function.

Parameters:

low - The low of the function.

center - The center of the function.

high - The high of the function.

Method Detail

activationFunction

public final void activationFunction(double[] x,
                                     int start,
                                     int size)

Implements the activation function. The array is modified according to the activation function being used. See the class description for more specific information on this type of activation function.

Specified by:

activationFunction in interface ActivationFunction

Parameters:

x - The input array to the activation function.

start - The starting index.

size - The number of values to calculate.

clone

public final ActivationFunction clone()

Specified by:

clone in interface ActivationFunction

Overrides:

clone in class Object

Returns:

A clone of this object.

derivativeFunction

public final double derivativeFunction(double b,
                                       double a)

Calculate the derivative. For performance reasons two numbers are provided. First, the value "b" is simply the number that we would like to calculate the derivative of. Second, the value "a", which is the value returned by the activation function, when presented with "b". We use two values because some of the most common activation functions make use of the result of the activation function. It is bad for performance to calculate this value twice. Yet, not all derivatives are calculated this way. By providing both the value before the activation function is applied ("b"), and after the activation function is applied("a"), the class can be constructed to use whichever value will be the most efficient.

Specified by:

derivativeFunction in interface ActivationFunction

Parameters:

b - The number to calculate the derivative of, the number "before" the activation function was applied.

a - The number "after" an activation function has been applied.

Returns:

The derivative.

getCenter

public final double getCenter()

Returns:

The center.

getHigh

public final double getHigh()

Returns:

The high value.

getLow

public final double getLow()

Returns:

The low value.

getParamNames

public final String[] getParamNames()

Specified by:

getParamNames in interface ActivationFunction

Returns:

The names of the parameters.

getParams

public final double[] getParams()

Specified by:

getParams in interface ActivationFunction

Returns:

The params for this activation function.

hasDerivative

public final boolean hasDerivative()

Specified by:

hasDerivative in interface ActivationFunction

Returns:

Returns true, this activation function has a derivative.

setCenter

public final void setCenter(double d)

Set the center of this function.

Parameters:

d - The center of this function.

setHigh

public final void setHigh(double d)

Set the high of this function.

Parameters:

d - The high of this function.

setLow

public final void setLow(double d)

Set the low of this function.

Parameters:

d - The low of this function.

setParam

public final void setParam(int index,
                           double value)

Set one of the params for this activation function.

Specified by:

setParam in interface ActivationFunction

Parameters:

index - The index of the param to set.

value - The value to set.

getFactoryCode

public String getFactoryCode()

Specified by:

getFactoryCode in interface ActivationFunction

Returns:

The string for the Encog factory code. Return null if you do not care to be support for creating of your activation through factory.