// $Id$
//
//    File: nnann_function_sigmoid.h
// Created: Tue Mar 22 23:21:37 EDT 2011
// Creator: davidl (on Darwin Amelia.local 9.8.0 i386)
//

#ifndef _nnann_function_sigmoid_
#define _nnann_function_sigmoid_

#include <cmath>
#include <nnann_function.h>

class nnann_function_sigmoid:public nnann_function{
	public:
		nnann_function_sigmoid(double k=1.0){this->k = k;}
		virtual ~nnann_function_sigmoid(){};

		void SetK(double k){this->k = k;}
		double GetK(void){return k;}
		std::string GetName(void){return "Sigmoid";}

		virtual double f(double x){
			return 1.0/(1.0 + std::exp(-k*x)); // standard sigmoid function
		}

		virtual double dfdx(double x){
			double my_f = f(x);
			return my_f*(1.0-my_f); // derivative of sigmoid
		}

	protected:
		double k;

};

#endif // _nnann_function_sigmoid_