atan2 (3)
Leading comments
Copyright 1993 David Metcalfe (david@prism.demon.co.uk)
and Copyright 2008, Linux Foundation, written by Michael Kerrisk
<mtk.manpages@gmail.com>
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NAME
atan2, atan2f, atan2l - arc tangent function of two variablesSYNOPSIS
#include <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
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.