function ExpEI(X: Double): Double;
Scaled exponential integral exp(-x)*Ei(x).
| # | Name | Description |
|---|---|---|
| 1 | X | Argument of the scaled exponential integral |
| 2 | must not be zero. |
Returns: Double - the scaled exponential integral exp(-x)*Ei(x).
Remarks:
Computes the exponentially scaled exponential integral
e^(-x) Ei(x),
which removes the dominant e^{x} growth of Ei for large positive x and decays like 1/x, avoiding overflow. For large x it tends to 0 from above. Domain: any real x \ne 0 (same singularity at the origin as Ei).
See Also: SpecialFuncs.EI, SpecialFuncs.E1