Arc tangent function of two variables

#include <math.h>double atan2(doubley, doublex);float atan2f(floaty, floatx);long double atan2l(long doubley, long doublex);

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.1-2001. The variant returning *double* also conforms to SVr4, 4.3BSD, C89.

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