The ATANH function returns the hyperbolic arc tangent of
a number, in radians. The ATANH and TANH functions are inverse operations.

>>-ATANH--(--expression--)-------------------------------------><
- expression
- An expression that returns a value of any built-in numeric data
type (except for DECFLOAT), character-string, or graphic-string data
type. A string argument is cast to double-precision floating point
before evaluating the function. For more information about converting
strings to double-precision floating point, see DOUBLE_PRECISION or DOUBLE. The value must be greater than
-1 and less than 1.
The data type of the result is double-precision floating
point. If the argument can be null, the result can be null; if the
argument is null, the result is the null value.