#include <Eigen/Core> USING_PART_OF_NAMESPACE_EIGEN using namespace std; int main() { typedef Matrix<SCALAR,Eigen::Dynamic,1> Vec; Vec v(SIZE); v.setZero(); v[0] = 1; v[1] = 2; for(int i = 0; i < 1000000; i++) { v.coeffRef(0) += v.sum() * SCALAR(1e-20); } cout << v.sum() << endl; }