Hinweis：Dieser Abschnitt ist nur in englischer Sprache verfügbar. Wir bitten um Ihr Verständnis.
3.5.1.3.34 Exp_integral
Definition:
\(E1 = exp\_integral(x)\) evaluates
- \[E_1(x)=\int_x^\infty \frac{e^{-u}}udu , x>0\]
The approximation is based on several Chebyshev expansions.
For more information please review the s13aac function in the NAG document.
Parameters:
- x (input, double)
- The argument x of the function.
- Constraint: x>0.0
- \[E1 (output, double)\]
- The approximation of the formula \(E_1(x)=\int_x^\infty \frac{e^{-u}}udu , x>0\)