ArcTan[z] gives the arc tangent of the complex number z.
ArcTan[x, y] gives the arc tangent of , taking into account which quadrant the point is in.
Mathematical function (see Section A.3.10).
All results are given in radians.
For real z, the results are always in the range to .
ArcTan[z] has branch cut discontinuities in the complex z plane running from to and to .
If x or y is complex, then ArcTan[x, y] gives . When , ArcTan[x, y] gives the number such that and .
See The Mathematica Book: Section 1.1.3 and Section 3.2.6.
See also: Arg.