ATAN(3) Linux Programmer's Manual ATAN(3)
atan, atanf, atanl - arc tangent function
#include <math.h> double atan(double x); float atanf(float x); long double atanl( long double x); Link with -lm. Feature Test Macro Requirements for glibc (see feature_test_macros(7)): atanf(), atanl(): _BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE >= 600 || _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L; or cc -std=c99
The atan() function calculates 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.
Multithreading (see pthreads(7)) The atan(), atanf(), and atanl() functions are thread-safe.
C99, POSIX.1-2001. The variant returning double also conforms to SVr4, 4.3BSD, C89.
acos(3), asin(3), atan2(3), carg(3), catan(3), cos(3), sin(3), tan(3)
This page is part of release 3.61 of the Linux man-pages project. A description of the project, and information about reporting bugs, can be found at http://www.kernel.org/doc/man-pages/. 2013-10-07 ATAN(3)
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