26 Numerics library [numerics]
26.9 Mathematical functions for floating-point types [c.math]
26.9.5 Mathematical special functions [sf.cmath]
26.9.5.14 Exponential integral [sf.cmath.expint]
double expint(double x);
float expintf(float x);
long double expintl(long double x);
Effects: These functions compute the exponential integral of their respective arguments x.
Returns:
![\[%
\mathsf{Ei}(x) =
- \int_{-x}^\infty \frac{e^{-t}}
{t } \, \mathsf{d}t
\;
\]](math/7484770320326636216.png)
where
x is x.