Linux manual pages Section 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);
 
[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>

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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)