atan - arc tangent function
#include <math.h> double atan(double x);
The atan() function computes the principal value of the arc tangent of x.
An application wishing to check for error situations should set errno to 0 before calling atan(). If errno is non-zero on return, or the return value is NaN, an error has occurred.
Upon successful completion, atan() returns the arc tangent of x in the range [-/2, /2] radians.
If x is NaN, NaN is returned and errno may be set to [EDOM].
If the result underflows, 0.0 is returned and errno may be set to [ERANGE].
The atan() function may fail if:
- The value of x is NaN.
- The result underflows.
No other errors will occur.
atan2(), isnan(), tan(), <math.h>.
Derived from Issue 1 of the SVID.