28 Numerics library [numerics]

28.7 Mathematical functions for floating-point types [c.math]

28.7.6 Mathematical special functions [sf.cmath]

28.7.6.15 Exponential integral [sf.cmath.expint]

floating-point-type expint(floating-point-type x); float expintf(float x); long double expintl(long double x);
Effects: These functions compute the exponential integral of their respective arguments x.
Returns: Ei(x), where Ei is given by Formula 28.35 and x is x.