atan, atanf, atanl – arc tangent function

USAGE
       #include <math.h>

       double atan(double x);
       float atanf(float x);
       long double atanl( long double x);

       Link with -lm.

DESCRIPTION
       The  atan() function calculates the arc tangent of x; that is the value
       whose tangent is x.

RETURN VALUE
       The atan() function returns the arc tangent in radians and the value is
       mathematically defined to be between -PI/2 and PI/2 (inclusive).

CONFORMING TO
       SVr4,  POSIX.1-2001,  4.3BSD,  C89.  The float and long double variants
       are C99 requirements.

SEE ALSO
       acos(3), asin(3), atan2(3), carg(3), catan(3), cos(3), sin(3), tan(3)