**atan**

SYNOPSIS
#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
DESCRIPTION
The atan() function calculates 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 tan-
gent 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.
CONFORMING TO
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)**
COLOPHON
This page is part of release 3.35 of the Linux man-pages project. A
description of the project, and information about reporting bugs, can
be found at http://man7.org/linux/man-pages/.
2010-09-20 **ATAN(3)**

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