R8035/BackwardEulerSolver.cpp
feaabd003240master

BackwardEulerSolver.cpp
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			//
			// Created by Pablo on 12/2/18.
			//

			#include "BackwardEuler.hpp"
			#include <cmath>

			#define THRESH 50 //Max iter for fixed point method


			BackwardEulerSolver::BackwardEulerSolver() {}

			BackwardEulerSolver::~BackwardEulerSolver() {}

			void BackwardEulerSolver::SolveEquation(std::ostream &stream) {
			double y_prev = GetInitialValue();
			double y_next;

			double t_prev = GetInitialTime();
			double t_next;

			double h = GetStepSize();
			int n = static_cast<int>(std::floor((GetFinalTime() - GetInitialTime()) / h));

			stream << t_prev << " " << y_prev << "\n";

			for (int i = 1; i <= n; ++i) {
			y_next = y_prev;
			t_next = t_prev + h;
			// Fixed point iteration
			for (int j = 1; j <= THRESH; ++j) {
			y_next = y_prev + h * RightHandSide(y_next, t_next);
			}

			stream << t_next << " " << y_next << "\n";
			y_prev = y_next;
			t_prev = t_next;
			}
			}