atan - Man Page
arc tangent function
Library
Math library (libm, -lm)
Synopsis
#include <math.h> double atan(double x); float atanf(float x); long double atanl(long double x);
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
atanf(), atanl():
_ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L || /* Since glibc 2.19: */ _DEFAULT_SOURCE || /* glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
Description
These functions calculate the principal value of the arc tangent of x; that is the value whose tangent is x.
Return Value
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.
Errors
No errors occur.
Attributes
For an explanation of the terms used in this section, see attributes(7).
Interface | Attribute | Value |
---|---|---|
atan(), atanf(), atanl() | Thread safety | MT-Safe |
Standards
C11, POSIX.1-2008.
History
C99, POSIX.1-2001.
The variant returning double also conforms to SVr4, 4.3BSD, C89.
See Also
acos(3), asin(3), atan2(3), carg(3), catan(3), cos(3), sin(3), tan(3)
Referenced By
acos(3), asin(3), atan2(3), cos(3), sin(3), tan(3).
The man pages atanf(3) and atanl(3) are aliases of atan(3).