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ATAN2
Section: Linux Programmer's Manual (3)
Updated: 20150419
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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 tangent 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 infinity, +pi (pi) is returned.
If
y
is a finite value greater (less) than 0, and
x
is positive infinity, +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 infinity, +3*pi/4 (3*pi/4) is returned.
If
y
is positive infinity (negative infinity) and
x
is positive infinity, +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  MTSafe

CONFORMING TO
C99, POSIX.12001, POSIX.12008.
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
manpages
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/manpages/.
Index
 NAME

 SYNOPSIS

 DESCRIPTION

 RETURN VALUE

 ERRORS

 ATTRIBUTES

 CONFORMING TO

 SEE ALSO

 COLOPHON

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