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 ALSO acos(3), asin(3), atan(3), carg(3), cos(3), sin(3), tan(3)

COLOPHON This page is part of release 3.22 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)