26 Numerics library [numerics]

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

double       comp_ellint_1(double k);
float        comp_ellint_1f(float k);
long double  comp_ellint_1l(long double k);

Effects: These functions compute the complete elliptic integral of the first kind of their respective arguments k.

Returns:

K (k) = F (k, π / 2), for | k | \leq 1,

where k is k.