05_pendulum.cpp

// compile with
// g++ ode_demo.cpp bla/calcinverse.cpp bla/exception.cpp bla/localheap.cpp -std=c++11 -o ode_demo -fmax-errors=2 -fdiagnostics-color=auto
//


// a simple linear algebra library
#include "bla/bla.hpp"
using namespace ngbla;
#include "ode.hpp"
#include "RK_orig.hpp"


using namespace ngbla;


class Pendulum_ODE_Function : public ODE_Function
{
	double g; //gravitation force
	double l; //pendulum länge
public:
	Pendulum_ODE_Function(double am, double ak) { g = am; l = ak; }

	//alpha, omega
	virtual void Eval(double t, const Vector<>& y, Vector<>& f) const
	{
		f(0) = y(1);
		f(1) = -(g/l) * sin(y(0));
	}
};


int main()
{
  ImplicitEuler impl_euler;
  
  ofstream out("Pendulum.txt");
  Pendulum_ODE_Function pen(1, 1);
  Vector<> y0(2);
  y0(0) = M_PI/2;
  y0(1) = 0;
  ODESolver(pen, impl_euler, 0, y0, 1000, 0.1, out);
  return 0;
}