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|man pages section 3: Extended Library Functions, Volume 2 Oracle Solaris 11 Information Library|
- arc tangent function
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 [-π/2,π/2] radians.
If x is NaN, NaN is returned.
If x is ±0, x is returned.
If x is ±Inf, ±π/2 is returned.
No errors are defined.
See attributes(5) for descriptions of the following attributes: