ATAN2

Section: Linux Programmer's Manual (3)
Updated: 2017-09-15
Index

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);`

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

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/xin radians; the return value is in the range [-pi, pi].

If yis +0 (-0) and xis less than 0, +pi (-pi) is returned.

If yis +0 (-0) and xis greater than 0, +0 (-0) is returned.

If yis less than 0 and xis +0 or -0, -pi/2 is returned.

If yis greater than 0 and xis +0 or -0, pi/2 is returned.

If either xor yis NaN, a NaN is returned.

If yis +0 (-0) and xis -0, +pi (-pi) is returned.

If yis +0 (-0) and xis +0, +0 (-0) is returned.

If yis a finite value greater (less) than 0, and xis negative infinity, +pi (-pi) is returned.

If yis a finite value greater (less) than 0, and xis positive infinity, +0 (-0) is returned.

If yis positive infinity (negative infinity), and xis finite, pi/2 (-pi/2) is returned.

If yis positive infinity (negative infinity) and xis negative infinity, +3*pi/4 (-3*pi/4) is returned.

If yis positive infinity (negative infinity) and xis 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 doublealso conforms to SVr4, 4.3BSD, C89.

acos(3), asin(3), atan(3), carg(3), cos(3), sin(3), tan(3)

NAME
SYNOPSIS
DESCRIPTION
RETURN VALUE
ERRORS
ATTRIBUTES
CONFORMING TO