c/numeric/complex/catan

@1-3@ Computes the complex arc tangent of with branch cuts outside the interval $[−i,+i]$ along the imaginary axis. @4@ Type-generic macro: If has type,  is called. if has type,  is called, if  has type ,  is called. If is real or integer, then the macro invokes the corresponding real function. If is imaginary, then the macro invokes the corresponding real version of the function atanh, implementing the formula $atan(iy) = i atanh(y)$, and the return type of the macro is imaginary.

Return value
If no errors occur, complex arc tangent of is returned, in the range of a strip unbounded along the imaginary axis and in the interval $[−π/2; +π/2]$ along the real axis.

Errors and special cases are handled as if the operation is implemented by.