Computes the arc tangent.
#include <math.h> float atanf (x) float x; long double atanl (x) long double x; double atan (x) double x;
The atanf, atanl, and atan subroutines compute the principal value of the arc tangent of the x parameter.
An application wishing to check for error situations should set the errno global variable to zero and call feclearexcept(FE_ALL_EXCEPT) before calling these functions. On return, if errno is nonzero or fetestexcept(FE_INVALID | FE_DIVBYZERO | FE_OVERFLOW | FE_UNDERFLOW) is nonzero, an error has occurred.
| x | Specifies the value to be computed. |
Upon successful completion, the atanf, atanl, and atan subroutines return the arc tangent of x in the range [-pi /2, pi/2] radians.
If x is NaN, a NaN is returned.
If x is 0, x is returned.
If x is ±Inf, ±x/2 is returned.
If x is subnormal, a range error may occur and x is returned.
The atan2f, atan2l, or atan2 Subroutine and atanh, atanhf, or atanhl Subroutine.
math.h in AIX 5L Version 5.2 Files Reference.