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## org.encog.engine.network.activation
Class ActivationLOG

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

All Implemented Interfaces:
  Serializable, Cloneable, ActivationFunction

    public class ActivationLOG

extends Object
implements ActivationFunction

An activation function based on the logarithm function. This type of activation function can be useful to prevent saturation. A hidden node of a neural network is said to be saturated on a given set of inputs when its output is approximately 1 or -1 "most of the time". If this phenomena occurs during training then the learning of the network can be slowed significantly since the error surface is very at in this instance.

Author:
  jheaton
See Also:
  Serialized Form

Constructor Summary
`ActivationLOG()` Construct the 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.
`String` | `getFactoryCode()`
`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

### ActivationLOG

    public ActivationLOG()

  Construct the activation 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:
    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 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:
    Return true, log 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 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.

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