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);

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.