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);
 
[Note] Note
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
atan2f(), atan2l():
_ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L || /* Since glibc 2.19:
*/ _DEFAULT_SOURCE || /* Glibc versions <= 2.19:
*/ _BSD_SOURCE || _SVID_SOURCE
[Note] Note

Link with −lm.

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 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 4.07 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 https://www.kernel.org/doc/man−pages/.


  Copyright 1993 David Metcalfe (davidprism.demon.co.uk)
and Copyright 2008, Linux Foundation, written by Michael Kerrisk
    <mtk.manpagesgmail.com>

%%%LICENSE_START(VERBATIM)
Permission is granted to make and distribute verbatim copies of this
manual provided the copyright notice and this permission notice are
preserved on all copies.

Permission is granted to copy and distribute modified versions of this
manual under the conditions for verbatim copying, provided that the
entire resulting derived work is distributed under the terms of a
permission notice identical to this one.

Since the Linux kernel and libraries are constantly changing, this
manual page may be incorrect or out-of-date.  The author(s) assume no
responsibility for errors or omissions, or for damages resulting from
the use of the information contained herein.  The author(s) may not
have taken the same level of care in the production of this manual,
which is licensed free of charge, as they might when working
professionally.

Formatted or processed versions of this manual, if unaccompanied by
the source, must acknowledge the copyright and authors of this work.
%%%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 (faithcs.unc.edu)
Modified 2002-07-27 by Walter Harms
(walter.harmsinformatik.uni-oldenburg.de)