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; 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 tan‐
gent 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 infin‐
ity, +pi (-pi) is returned.
If y is a finite value greater (less) than 0, and x is positive infin‐
ity, +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 infin‐
ity, +3*pi/4 (-3*pi/4) is returned.
If y is positive infinity (negative infinity) and x is positive infin‐
ity, +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 ALSOacos(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)
