org.encog.engine.network.activation

Class ActivationSigmoid

java.lang.Object

org.encog.engine.network.activation.ActivationSigmoid

All Implemented Interfaces:

java.io.Serializable, java.lang.Cloneable, ActivationFunction

public class ActivationSigmoid
extends java.lang.Object
implements ActivationFunction

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.

See Also:

Serialized Form

Constructor Summary

Constructors

Constructor and Description
ActivationSigmoid() Construct a basic sigmoid function, with a slope of 1.

Method Summary

Modifier and Type	Method and Description
void	activationFunction(double[] x, int start, int size) Implements the activation function.
ActivationFunction	clone()
double	derivativeFunction(double b, double a) Calculate the derivative.
java.lang.String	getFactoryCode()
java.lang.String	getLabel()
java.lang.String[]	getParamNames()
double[]	getParams()
boolean	hasDerivative()
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

Constructor Detail

ActivationSigmoid

public ActivationSigmoid()

Construct a basic sigmoid function, with a slope of 1.

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 java.lang.Object

Returns:

The object cloned;

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.

getParamNames

public final java.lang.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:

True, sigmoid has a derivative.

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 java.lang.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.

getLabel

public java.lang.String getLabel()

Specified by:

getLabel in interface ActivationFunction

Returns:

The human-friendly name for this activation