Array<double,1,3> x(8,-25,3),
                  y(1./3.,0.5,-2.);
cout << "atan2([" << x << "], [" << y << "]) = " << x.atan2(y) << endl; // using ArrayBase::pow
cout << "atan2([" << x << "], [" << y << "] = " << atan2(x,y) << endl; // using Eigen::pow