atan, atanf, atanl - arc tangent function
Math library (
libm,
-lm)
#include <math.h>
double atan(double x);
float atanf(float x);
long double atanl(long double x);
atanf(),
atanl():
_ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
|| /* Since glibc 2.19: */ _DEFAULT_SOURCE
|| /* glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
These functions calculate the principal value of the arc tangent of
x;
that is the value whose tangent is
x.
On success, these functions return the principal value of the arc tangent of
x in radians; the return value is in the range [-pi/2, pi/2].
If
x is a NaN, a NaN is returned.
If
x is +0 (-0), +0 (-0) is returned.
If
x is positive infinity (negative infinity), +pi/2 (-pi/2) is returned.
No errors occur.
For an explanation of the terms used in this section, see
attributes(7).
Interface |
Attribute |
Value |
atan (), atanf (), atanl () |
Thread safety |
MT-Safe |
C99, POSIX.1-2001, POSIX.1-2008.
The variant returning
double also conforms to SVr4, 4.3BSD.
acos(3),
asin(3),
atan2(3),
carg(3),
catan(3),
cos(3),
sin(3),
tan(3)