.\" Copyright 1993 David Metcalfe (david@prism.demon.co.uk)
.\" and Copyright 2008, Linux Foundation, written by Michael Kerrisk
.\"     <mtk.manpages@gmail.com>
.\"
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.\" manual provided the copyright notice and this permission notice are
.\" preserved on all copies.
.\"
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.\" manual under the conditions for verbatim copying, provided that the
.\" entire resulting derived work is distributed under the terms of a
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.\"
.\" Since the Linux kernel and libraries are constantly changing, this
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.\" responsibility for errors or omissions, or for damages resulting from
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.\" %%%LICENSE_END
.\"
.\" References consulted:
.\"     Linux libc source code
.\"     Lewine's _POSIX Programmer's Guide_ (O'Reilly & Associates, 1991)
.\"     386BSD man pages
.\" Modified 1993-07-24 by Rik Faith (faith@cs.unc.edu)
.\" Modified 2002-07-27 by Walter Harms
.\" 	(walter.harms@informatik.uni-oldenburg.de)
.\"
.TH ATAN2 3  2016-03-15 "" "Linux Programmer's Manual"
.SH NAME
atan2, atan2f, atan2l \- arc tangent function of two variables
.SH SYNOPSIS
.nf
.B #include <math.h>

.BI "double atan2(double " y ", double " x );
.BI "float atan2f(float " y ", float " x );
.BI "long double atan2l(long double " y ", long double " x );

.fi
Link with \fI\-lm\fP.
.sp
.in -4n
Feature Test Macro Requirements for glibc (see
.BR feature_test_macros (7)):
.in
.sp
.ad l
.BR atan2f (),
.BR atan2l ():
.RS
_ISOC99_SOURCE || _POSIX_C_SOURCE\ >=\ 200112L
    || /* Since glibc 2.19: */ _DEFAULT_SOURCE
    || /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
.RE
.ad b
.SH DESCRIPTION
These functions calculate the principal value of the arc tangent of
.IR y/x ,
using the signs of the two arguments to determine
the quadrant of the result.
.SH RETURN VALUE
On success, these functions return the principal value of the arc tangent of
.IR y/x
in radians; the return value is in the range [\-pi,\ pi].

If
.I y
is +0 (\-0) and
.I x
is less than 0, +pi (\-pi) is returned.

If
.I y
is +0 (\-0) and
.I x
is greater than 0, +0 (\-0) is returned.

If
.I y
is less than 0 and
.I x
is +0 or \-0, \-pi/2 is returned.

If
.I y
is greater than 0 and
.I x
is +0 or \-0, pi/2 is returned.

.\" POSIX.1 says:
.\" If
.\" .I x
.\" is 0, a pole error shall not occur.
.\"
If either
.I x
or
.I y
is NaN, a NaN is returned.

.\" POSIX.1 says:
.\" If the result underflows, a range error may occur and
.\" .I y/x
.\" should be returned.
.\"
If
.I y
is +0 (\-0) and
.I x
is \-0, +pi (\-pi) is returned.

If
.I y
is +0 (\-0) and
.I x
is +0, +0 (\-0) is returned.

If
.I y
is a finite value greater (less) than 0, and
.I x
is negative infinity, +pi (\-pi) is returned.

If
.I y
is a finite value greater (less) than 0, and
.I x
is positive infinity, +0 (\-0) is returned.

If
.I y
is positive infinity (negative infinity), and
.I x
is finite,
pi/2 (\-pi/2) is returned.

If
.I y
is positive infinity (negative infinity) and
.I x
is negative infinity, +3*pi/4 (\-3*pi/4) is returned.

If
.I y
is positive infinity (negative infinity) and
.I x
is positive infinity, +pi/4 (\-pi/4) is returned.
.\"
.\" POSIX.1 says:
.\" If both arguments are 0, a domain error shall not occur.
.SH ERRORS
No errors occur.
.\" POSIX.1 documents an optional underflow error
.\" glibc 2.8 does not do this.
.SH ATTRIBUTES
For an explanation of the terms used in this section, see
.BR attributes (7).
.TS
allbox;
lbw28 lb lb
l l l.
Interface	Attribute	Value
T{
.BR atan2 (),
.BR atan2f (),
.BR atan2l ()
T}	Thread safety	MT-Safe
.TE
.SH CONFORMING TO
C99, POSIX.1-2001, POSIX.1-2008.

The variant returning
.I double
also conforms to
SVr4, 4.3BSD, C89.
.SH SEE ALSO
.BR acos (3),
.BR asin (3),
.BR atan (3),
.BR carg (3),
.BR cos (3),
.BR sin (3),
.BR tan (3)
.SH COLOPHON
This page is part of release 4.10 of the Linux
.I man-pages
project.
A description of the project,
information about reporting bugs,
and the latest version of this page,
can be found at
\%https://www.kernel.org/doc/man\-pages/.