ATAN2(3) | Linux Programmer's Manual | ATAN2(3) |

# NAME

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

**#include**

<math.h>

<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

The**atan2**() function calculates 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].

*y*is +0 (-0) and

*x*is less than 0, +pi (-pi) is returned.

*y*is +0 (-0) and

*x*is greater than 0, +0 (-0) is returned.

*y*is less than 0 and

*x*is +0 or -0, -pi/2 is returned.

*y*is greater than 0 and

*x*is +0 or -0, pi/2 is returned.

*x*or

*y*is NaN, a NaN is returned.

*y*is +0 (-0) and

*x*is -0, +pi (-pi) is returned.

*y*is +0 (-0) and

*x*is +0, +0 (-0) is returned.

*y*is a finite value greater (less) than 0, and

*x*is negative infinity, +pi (-pi) is returned.

*y*is a finite value greater (less) than 0, and

*x*is positive infinity, +0 (-0) is returned.

*y*is positive infinity (negative infinity), and

*x*is finite, pi/2 (-pi/2) is returned.

*y*is positive infinity (negative infinity) and

*x*is negative infinity, +3*pi/4 (-3*pi/4) is returned.

*y*is positive infinity (negative infinity) and

*x*is positive infinity, +pi/4 (-pi/4) is returned.

# ERRORS

No errors occur.# CONFORMING TO

C99, POSIX.1-2001. 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 3.53 of the Linux*man-pages*project. A description of the project, and information about reporting bugs, can be found at http://www.kernel.org/doc/man-pages/.

2010-09-20 |