//FeedforwardNode.h
//
//Declaration of abstract base class for feedforward neural network nodes.
//FeedforwardNode inherits functionality from the abstract Node class
//
//
//Copyright 1998 Michael J. Wax
//You may use this code as is, or incorporate it in another program,
//as long as proper attribution is given.  However, I make no warranties,
//express or implied, regarding the performance of this code, its freedom from
//error, or its suitability for use in a given application.
//Questions or suggestions?  Contact me at neural@michaelwax.com
//

#ifndef FEEDFN_H
#define FEEDFN_H

#include "Node.cpp"

class FeedforwardNode : public Node<double> {
  public:
    FeedforwardNode ();

    //copy constructor
    FeedforwardNode (const FeedforwardNode &fnode);

    //assignment operator
    FeedforwardNode& operator= (const FeedforwardNode &fnode);

    //--------------calculation of the node activation---------------
    //"Activation" calculates the net input of the nodes, and then calls "ActivationFunction."
    //The threshold has a default value of zero, and so need not be entered.
    //
    double activation (double threshold);

    //"firstHiddenLayerActivation" acts on an array of input values (*inputVector), rather than on the outputs of
    // any lower level nodes, and is useful when there are multiple input patterns.
    //The threshold variable has a default value of zero.
    //
    double firstHiddenLayerActivation (double *inputVector, double threshold);

    //ActivationFunction uses a logistic function (1/(1+e^-(net-threshold)) to calculate the output of the node;
    // overload this to use a different function (e.g., a lookup-table-based function for speed).
    double activationFunction (double net, double threshold);

    //-------------error calculation functions------------
    //These pure virtual functions are for use by derived classes for network evaluation/training.

    //Calculate the error of a node.
    //For hidden layer nodes, this function will assign responsibility for the error in the output nodes.
    virtual double calculateError () = 0;

    //Calculate the error of an output node.
    virtual double calculateOutputNodeError (double actualValue) = 0;

    //------------------readers and writers--------------------------
    //Read the error in the node output.  CAREFUL:  the stored value may not be updated.
    double readError();

  protected:
    double error;

};

#endif