RungeKuttaSolver.cpp
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RungeKuttaSolver.cpp
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			/*
			* RungeKuttaSolver.cpp
			*
			* Created on: Oct 25, 2012
			* Author: rpopescu
			*/

			#include "RungeKuttaSolver.hpp"

			#include <cmath>

			RungeKuttaSolver::RungeKuttaSolver()
			{}

			RungeKuttaSolver::~RungeKuttaSolver()
			{}

			void RungeKuttaSolver::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) {
			double k1 = h * RightHandSide(y_prev, t_prev);
			double k2 = h * RightHandSide(y_prev + 0.5 * k1, t_prev + 0.5 * h);
			double k3 = h * RightHandSide(y_prev + 0.5 * k2, t_prev + 0.5 * h);
			double k4 = h * RightHandSide(y_prev + k3, t_prev + h);

			y_next = y_prev + 1.0/6.0 * (k1 + 2 * k2 + 2 * k3 + k4);
			t_next = t_prev + h;

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