**atan2f**

**ATAN2(3)** Linux Programmer's Manual **ATAN2(3)**
NAME
atan2, atan2f, atan2l - arc tangent function of two variables
SYNOPSIS
#include <math.h>
double atan2(double y, double x);
float atan2f(float y, float x);
long double atan2l(long double y, long double x);
Link with -lm.
Feature Test Macro Requirements for glibc (see **feature_test_macros(7)**):
atan2f(), atan2l():
_BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE >= 600 ||
_ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L;
or cc -std=c99
DESCRIPTION
These functions calculate the principal value of the arc tangent of
y/x, using the signs of the two arguments to determine the quadrant of
the result.
RETURN VALUE
On success, these functions return the principal value of the arc tan-
gent of y/x in radians; the return value is in the range [-pi, pi].
If y is +0 (-0) and x is less than 0, +pi (-pi) is returned.
If y is +0 (-0) and x is greater than 0, +0 (-0) is returned.
If y is less than 0 and x is +0 or -0, -pi/2 is returned.
If y is greater than 0 and x is +0 or -0, pi/2 is returned.
If either x or y is NaN, a NaN is returned.
If y is +0 (-0) and x is -0, +pi (-pi) is returned.
If y is +0 (-0) and x is +0, +0 (-0) is returned.
If y is a finite value greater (less) than 0, and x is negative infin-
ity, +pi (-pi) is returned.
If y is a finite value greater (less) than 0, and x is positive infin-
ity, +0 (-0) is returned.
If y is positive infinity (negative infinity), and x is finite, pi/2
(-pi/2) is returned.
If y is positive infinity (negative infinity) and x is negative infin-
ity, +3*pi/4 (-3*pi/4) is returned.
If y is positive infinity (negative infinity) and x is positive infin-
ity, +pi/4 (-pi/4) is returned.
ERRORS
No errors occur.
ATTRIBUTES
For an explanation of the terms used in this section, see
**attributes(7)**.
+-----------------------------+---------------+---------+
|Interface | Attribute | Value |
+-----------------------------+---------------+---------+
|atan2(), atan2f(), atan2l() | Thread safety | MT-Safe |
+-----------------------------+---------------+---------+
CONFORMING TO
C99, POSIX.1-2001, POSIX.1-2008.
The variant returning double also conforms to SVr4, 4.3BSD, C89.
SEE ALSO
**acos(3)**, **asin(3)**, **atan(3)**, **carg(3)**, **cos(3)**, **sin(3)**, **tan(3)**
COLOPHON
This page is part of release 4.04 of the Linux man-pages project. A
description of the project, information about reporting bugs, and the
latest version of this page, can be found at
http://www.kernel.org/doc/man-pages/.
2015-04-19 **ATAN2(3)**

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