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);
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; 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].
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.
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 3.24 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/.
2008-11-20 ATAN2(3)