NAME  SYNOPSIS  DESCRIPTION  RETURN VALUE  ERRORS  CONFORMING TO  SEE ALSO  COLOPHON 

ATAN2(3) Linux Programmer's Manual ATAN2(3)
atan2, atan2f, atan2l  arc tangent function of two variables
#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
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.
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.
No errors occur.
C99, POSIX.12001. The variant returning double also conforms to SVr4, 4.3BSD, C89.
acos(3), asin(3), atan(3), carg(3), cos(3), sin(3), tan(3)
This page is part of release 3.73 of the Linux manpages project. A
description of the project, information about reporting bugs, and the
latest version of this page, can be found at
http://www.kernel.org/doc/manpages/.
20100920 ATAN2(3)
Copyright and license for this manual page