/*
 * File:        ActivationFunction.java
 * Author:      Justin Basilico
 * Course:      PO CS 152: Neural Networks
 * Assignment:  Final Project
 * Updated:     2001.12.18
 * Created:     2001.12.04
 *
 * Description:
 * This file contains the ActivationFunction interface, which is an interface
 * that is used to describe an activation that is used in a NeuralNetwork to
 * get the activation value of a unit in the network given the input
 * activation into the unit.
 *
 * Copyright:    Justin Basilico (2001).
 */

import java.io.Serializable;

/**
 * ActivationFunction interface
 *
 * This interface is to be implemented by a class that has an activation
 * function for units in a neural network. The function is defined to be a
 * function from the real numbers to the real numbers. The input number is the
 * total input into the unit in the network. The value returned should will be
 * used as the activation of that unit. The function to implement that does
 * this is getUnitActivation(double) which takes a double and returns a
 * double.
 *
 * The interface extends Serializable so that the function can be saved with a
 * NeuralNetwork that uses it.
 *
 * @author  Justin Basilico
 * @version 2001.12.18
 * @see     NeuralNetwork
 */
public interface ActivationFunction
    extends Serializable
{
    /**
     * getUnitActivation
     *
     * This method takes a double input that is the total input to a unit in a
     * neural network and returns the double activation value for that unit
     * from the given input.
     *
     * @param  input The value of the input to a unit, as a double.
     * @return The activation for the unit given the input value, as a double.
     */
    public double getUnitActivation(
        double              input);         // Total input to unit.
}