atanh

Calculates inverse hyperbolic tangent of a double value.

Special cases:

• If the argument is NaN, then the result is NaN.

• If the argument is zero, then the result is a zero with the same sign as the argument.

• If the argument is +1, then the result is positive infinity.

• If the argument is -1, then the result is negative infinity.

• If the argument's absolute value is greater than 1, then the result is NaN.