Synopsis
#include <math.h>
float atanf(float x);
Description

atanf returns the principal value, in radians, of the inverse circular tangent of x. The principal value lies in the interval [-½?, +½?] radians.

Portability

atanf conforms to ISO/IEC 9899:1990 (C90) and ISO/IEC 9899:1999 (C99).