Returns the arc-tangent of its argument.
Implemented by: bw32, Gambas, minibasicmm
With variations:
Also written as: ATN, Atn
The arc-tangent is the inverse of the tangent function, i.e., 1 / TAN.
In most (if not all) BASIC implementations the return value is in radians.
In Gambas, ATan is a synonym for Atn.