##### Synopsis

    #include <math.h>
    double atan2(double y, double x);

##### Description

atan2 returns the value, in radians, of the inverse circular tangent of y divided by x using the signs of x and y to compute the quadrant of the return value. The principal value lies in the interval [-PI/2, +PI/2] radians.

##### Fast math library behavior

If x = y = 0, errno is set to EDOM and atan2 returns HUGE_VAL.

##### IEC 60559 math library behavior

atan2f(x, NaN) is NaN
atan2f(NaN, x) is NaN
atan2f(±0, +(anything but NaN)) is ±0
atan2f(±0, -(anything but NaN)) is ±?
atan2f(±(anything but 0 and NaN), 0) is ±?/2
atan2f(±(anything but ? and NaN), +?) is ±0
atan2f(±(anything but ? and NaN), -?) is ±?
atan2f(±?, +?) is ±?/4
atan2f(±?, -?) is ±3?/4
atan2f(±?, (anything but 0, NaN, and ?)) is ±?/2

##### Portability

atan2 conforms to ISO/IEC 9899:1990 (C90) and ISO/IEC 9899:1999 (C99).

##### See Also

atan