The
atan2() function, if successful, returns the arc tangent of
y/x in the range [-π, +π] radians. If both
x and
y are zero, the global variable
errno is set to
EDOM. On the VAX:
atan2(y, x) :=
atan(y/x)
if x > 0,
sign(y)*(π - atan(\*(Bay/x\*(Ba))
if x < 0,
sign(y)*\*(Pi/2
if x = 0 y.