darkhistory.utilities.exp_expn¶
- darkhistory.utilities.exp_expn(n, x)¶
Returns \(e^x E_n(x)\).
The exponential integral \(E_n(x)\) is defined as
\[E_n(x) \equiv \int_1^\infty dt\, \frac{e^{-xt}}{t^n}\]Circumvents overflow error in
np.expby expanding the exponential integral in a series to the 5th or 6th order.- Parameters:
- n{1,2}
The order of the exponential integral.
- xndarray
The argument of the function.
- Returns:
- ndarray
The value of \(e^x E_n(x)\).