## table of contents

- stretch 4.10-2
- testing 4.16-2
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ATAN2(3) | Linux Programmer's Manual | ATAN2(3) |

# NAME¶

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

Link with#include <math.h>double atan2(doubley, doublex);float atan2f(floaty, floatx);long double atan2l(long doubley, long doublex);

*-lm*.

Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

**atan2f**(), **atan2l**():

# 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 4.10 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/.

2016-03-15 |