This is to calculate
$$\Phi_l(x)=\frac{\int_0^x s^le^{-s}ds}{x^{l+1}},\hspace{0.5cm}l=0,1,2.$$
This function is well defined even when x=0. However, it is numerical chanllenging to calculate it when x is small. So when
\(|x|\le \code{eps}\) we approximate this function and the absolute error is \(\code{eps}^5\).