/* This file is part of the Palabos library.
 *
 * The Palabos softare is developed since 2011 by FlowKit-Numeca Group Sarl
 * (Switzerland) and the University of Geneva (Switzerland), which jointly
 * own the IP rights for most of the code base. Since October 2019, the
 * Palabos project is maintained by the University of Geneva and accepts
 * source code contributions from the community.
 * 
 * Contact:
 * Jonas Latt
 * Computer Science Department
 * University of Geneva
 * 7 Route de Drize
 * 1227 Carouge, Switzerland
 * jonas.latt@unige.ch
 *
 * The most recent release of Palabos can be downloaded at 
 * <https://palabos.unige.ch/>
 *
 * The library Palabos is free software: you can redistribute it and/or
 * modify it under the terms of the GNU Affero General Public License as
 * published by the Free Software Foundation, either version 3 of the
 * License, or (at your option) any later version.
 *
 * The library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU Affero General Public License for more details.
 *
 * You should have received a copy of the GNU Affero General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
*/

#include <cmath>

#include "functions.h"

#ifndef NEWTON_RAPHSON_H
#define NEWTON_RAPHSON_H


/** This class is a Newton-Raphson root finding solver.
 * It find y such that F(y)=0. It takes the function type as template
 * parameter and F(y), F'(y), the tolerance and the maximum iterations
 * the user allows in order for the NR solver to find the root.
 */

template <typename T>
class NewtonRaphson : public Function<T>
{
public :
	NewtonRaphson(FunctionAndDerivative<T> *function_, T tol_, int maxIter_)
		: function(function_), tol(tol_), maxIter(maxIter_)
	{   }
	
	virtual T operator()(T y) const 
	{
		T root0 = T();
		T root = T();
// 		std::cout << root0 << std::endl;
		for (int iPop = 0; iPop < maxIter; ++iPop)
		{
			root = root0 - (*(function))(y, root0) / function->derivative(y, root0);
// 			std::cout << std::fabs((root - root0)) << std::endl;
			if ((std::fabs((root - root0)/root0) < tol) || (root-root0) == T())
			{
// 				std::cout << root << std::endl;
				return root;
			}
			root0 = root;
		}
		
		std::cout << "Error Newton-Raphson never converged." << std::endl;
		exit(1);
        
		return root;
    }
	
private :
	FunctionAndDerivative<T> *function;
	T tol;
	int maxIter;
};

#endif
