org.encog.engine.network.activation
Class ActivationSigmoid

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

All Implemented Interfaces:

Serializable, Cloneable, ActivationFunction

public class ActivationSigmoid
extends 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

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

Method Summary

void	activationFunction(double[] x, int start, int size) Implements the activation function.
ActivationFunction	clone()
double	derivativeFunction(double x) Calculate the derivative of the activation.
String	getOpenCLExpression(boolean derivative) Returns the OpenCL expression for this activation function.
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

clone

public ActivationFunction clone()

Specified by:

clone in interface ActivationFunction

Overrides:

clone in class Object

Returns:

The object cloned;

hasDerivative

public boolean hasDerivative()

Specified by:

hasDerivative in interface ActivationFunction

Returns:

True, sigmoid has a derivative.

activationFunction

public 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.

derivativeFunction

public double derivativeFunction(double x)

Calculate the derivative of the activation. It is assumed that the value d, which is passed to this method, was the output from this activation. This prevents this method from having to recalculate the activation, just to recalculate the derivative. The array is modified according derivative of the activation function being used. See the class description for more specific information on this type of activation function. Propagation training requires the derivative. Some activation functions do not support a derivative and will throw an error.

Specified by:

derivativeFunction in interface ActivationFunction

Parameters:

x - The input array to the activation function.

Returns:

The derivative.

getParamNames

public String[] getParamNames()

Specified by:

getParamNames in interface ActivationFunction

Returns:

The names of the parameters.

getParams

public double[] getParams()

Specified by:

getParams in interface ActivationFunction

Returns:

The params for this activation function.

setParam

public 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.

getOpenCLExpression

public String getOpenCLExpression(boolean derivative)

Returns the OpenCL expression for this activation function.

Specified by:

getOpenCLExpression in interface ActivationFunction

Parameters:

derivative - True if we want the derivative, false otherwise.

Returns:

The OpenCL expression for this activation function.