int main(
int argc,
char** argv)
{
x.setZero();
double mass = 1.0;
double d = 0.01;
std::shared_ptr<Masspoint> masspoint(
new Masspoint(mass, d));
size_t nSteps = 1000;
std::cout << "state after integration: " << x.transpose() << std::endl;
return 0;
}