2017-09-15

Aliases: atan2f(3), atan2f(3), atan2f(3), atan2f(3), atan2f(3), atan2f(3), atan2f(3), atan2f(3), atan2f(3), atan2f(3), atan2l(3), atan2l(3), atan2l(3), atan2l(3), atan2l(3), atan2l(3), atan2l(3), atan2l(3), atan2l(3), atan2l(3)

### manpages-dev

Manual pages about using GNU/Linux for development

### man-pages

Linux kernel and C library user-space interface documentation

## NAME

atan2, atan2f, atan2l - arc tangent function of two variables

## SYNOPSIS

#include <math.h>

double atan2(doubley, doublex);float atan2f(floaty, floatx);long double atan2l(long doubley, long doublex);

Link with

*-lm*.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

|| /* Since glibc 2.19: */ _DEFAULT_SOURCE

|| /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE

## 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 |

Thread safety | MT-Safe |

## CONFORMING TO

C99, POSIX.1-2001, POSIX.1-2008.

The variant returning

*double*also conforms to SVr4, 4.3BSD, C89.## COLOPHON

This page is part of release 5.00 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/.