javax.datamining.algorithm.feedforwardneuralnet
Class ActivationFunction

java.lang.Object
  |
  +--javax.datamining.Enum
        |
        +--javax.datamining.algorithm.feedforwardneuralnet.ActivationFunction

All Implemented Interfaces:

java.lang.Comparable, java.io.Serializable

public class ActivationFunction

extends Enum

The enumeration AcivationFunction indicates the type of activation function used by the neural layer. The activation function computes the activation state of the neuron based on its inputs. For a single neuron, activation can be computed as a transform of the sum of the neural inputs times the weights on those inputs, plus the bias:
XZ = Sum(w(i) * input(i)) + bias
Y = output(j) = activation(XZ)

Note that the neural inputs may be outputs from the previous layer.

The following is the list of activation functions defined in JDM.

• systemDefault - The static, vendor-defined default option. This option may be different according to the context. Vendors must document the system default for each context.
• systemDetermined - The vendor implementation selects an option. The implementation may take into account, e.g., settings or data to determine an appropriate option. As such, this selection is expected to occur dynamically at runtime. Vendors must document the expected behavior.
• linearIdentity - The linear function y=x.
• logistic - The sigmoid function Y = 1/(1 + exp(-aX)).
• hyperbolicTangent - The hyperbolic tangent function Y = tanh(X) = (exp(X) - exp(-X))/(exp(X) + exp(X))
• sign - The sign function Y = 1 if X >= 0; Y = 0 if X < 0.
• symmetricSign - The symmetric sign function Y = 1 if X >= 0; Y = -1 if X <0.
• softMax - The softmax function Y_j = exp(X_j)/Sum[i in 1..n](exp(X_i)).

The following is a list of activation functions that are not defined in JDM, but are reserved. (from PMML 2.1)

• threshold : activation(Z) = if Z>threshold then 1 else 0
• tanh : activation(Z) = (1 - exp(-2Z))/(1+exp(-2Z))
• identity : activation(Z) = Z
• exponential : activation(Z) = exp(Z)
• reciprocal : activation(Z) = 1/Z
• square : activation(Z) = Z*Z
• gauss : activation(Z) = exp(-(Z*Z))
• sine : activation(Z) = sin(Z)
• elliot : activation(Z) = Z/(1+|Z|)
• arctan : activation(Z) = 2 * arctan(Z)P_i
• radialBasis : activation(Z) = exp(-(Sum_i (output(i) - C_i)^2) / (2*Width^2)) where the sum is taken over all input units, C_i are the coordinates of the center in place of the weights, and Width is the width of the radial basis function unit stored in Neuron element.

Author:

JSR-73 Java Data Mining Expert Group

See Also:

Serialized Form

Field Summary

static ActivationFunction	hyperbolicTangent
static ActivationFunction	linearIdentity
static ActivationFunction	logistic
static ActivationFunction	sign
static ActivationFunction	softMax
static ActivationFunction	symmetricSign
static ActivationFunction	systemDefault
static ActivationFunction	systemDetermined

Method Summary

static void	addExtension(java.lang.String name) Adds a vendor extension name to ActivationFunction.
static ActivationFunction	valueOf(java.lang.String name) Returns an instance of ActivationFunction corresponding to the specified name.
static ActivationFunction[]	values() Returns a list of all ActivationFunction enumerations defined.

Methods inherited from class javax.datamining.Enum

compareTo, equals, name

Methods inherited from class java.lang.Object

getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

hyperbolicTangent

public static final ActivationFunction hyperbolicTangent

linearIdentity

public static final ActivationFunction linearIdentity

logistic

public static final ActivationFunction logistic

sign

public static final ActivationFunction sign

softMax

public static final ActivationFunction softMax

symmetricSign

public static final ActivationFunction symmetricSign

systemDefault

public static final ActivationFunction systemDefault

systemDetermined

public static final ActivationFunction systemDetermined

Method Detail

addExtension

public static void addExtension(java.lang.String name)
                         throws JDMException

Adds a vendor extension name to ActivationFunction.

Parameters:

name - The name of the unique vendor extension

Throws:

JDMException - When name is an invalid string or redundant to existing standard enums.

valueOf

public static ActivationFunction valueOf(java.lang.String name)
                                  throws JDMException

Returns an instance of ActivationFunction corresponding to the specified name.

Parameters:

name - The name of the enumeration value

Returns:

ActivationFunction - The instance of the specified enumeration.

Throws:

JDMException - When name is not valid.

values

public static ActivationFunction[] values()

Returns a list of all ActivationFunction enumerations defined.

Returns:

ActivationFunction[]