Double E1(Double X)
Exponential integral E1(x) = -Ei(-x).
| # | Name | Description |
|---|---|---|
| 1 | X | Argument of the exponential integral |
| 2 | must be greater than zero. |
Returns: Double - the exponential integral E1(x) = -Ei(-x).
Remarks:
Computes the exponential integral of the first kind,
E_1(x)=integral _x^(inf)(e^(-t))/t dt=-Ei(-x),
defined and positive for x > 0, decreasing monotonically from +\infty at x\to 0^+ toward 0 as x\to\infty (asymptotically e^{-x}/x). Domain: real x > 0.
See Also: SpecialFuncs.EI, SpecialFuncs.ExpEI