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/////////////////////////////////////////////////////////////////////////////
//
// NNActivation.h
//
// all the activation functions of the neurons
//
// header file
//
// Copyright (c) 2005 Georg Holzmann <grh@gmx.at>
//
// This program is free software; you can redistribute it and/or
// modify it under the terms of the GNU General Public License
// as published by the Free Software Foundation; either version 2
// of the License, or (at your option) any later version.
//
/////////////////////////////////////////////////////////////////////////////
#ifndef _INCLUDE_ACTIVATION_NET__
#define _INCLUDE_ACTIVATION_NET__
#include <math.h>
namespace TheBrain
{
//------------------------------------------------------
/* implementation of the different activation functions
* and it's derivations
*/
/* Linear activation function.
* span: -inf < y < inf
* y = x
*/
#define LINEAR 0
/* Sigmoid activation function.
* span: 0 < y < 1
* y = 1/(1 + exp(-x)), y' = y*(1 - y)
*/
#define SIGMOID 1
/* Symmetric sigmoid activation function, aka. tanh.
* span: -1 < y < 1
* y = tanh(x) = 2/(1 + exp(-2*x)) - 1, d = 1-(y*y)
*/
#define TANH 2
// linear function
float act_linear(float value)
{ return value; }
// derivation of the linear function
float act_linear_derive(float value)
{ return 1; }
// sigmoid function
float act_sigmoid(float value)
{ return (1.0f/(1.0f + exp(-value))); }
// derivation of the sigmoid function
float act_sigmoid_derive(float value)
{ return (value * (1.0f - value)); }
// tanh function
float act_tanh(float value)
{ return (2.0f/(1.0f + exp(-2.0f * value)) - 1.0f); }
// derivation of the tanh function
float act_tanh_derive(float value)
{ return (1.0f - (value*value)); }
} // end of namespace
#endif // _INCLUDE_ACTIVATION_NET__
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