
ATAN2(3) Linux Programmer's Manual ATAN2(3)
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 
_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 radi
ans; 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.12001. 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 3.55 of the Linux manpages project. A description of the
project, and information about reporting bugs, can be found at
http://www.kernel.org/doc/manpages/.
20100920 ATAN2(3) 
