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c99 [ flag... ] file... -lm [ library... ] #include <math.h>
double atan(double x);
float atanf(float x);
long double atanl(long double x);
These functions compute the principal value of the arc tangent of x.
Upon successful completion, these functions return the arc tangent of x in the range [-pi/2,pi/2] radians.
If x is NaN, NaN is returned.
If x is ±0, x is returned.
If x is ±Inf, ±pi/2 is returned.
See attributes(5) for descriptions of the following attributes:
ATTRIBUTE TYPE | ATTRIBUTE VALUE |
Interface Stability | Standard |
MT-Level | MT-Safe |
atan2(3M), isnan(3M), math.h(3HEAD), tan(3M), attributes(5), standards(5)