atanh function
Return the inverse hyperbolic tangent of complex.
There are two branch cuts: One extends from 1 along the real axis to ∞,
continuous from below. The other extends from -1 along the real axis to -∞,
continuous from above.
Implementation
Complex<num, num> atanh(Complex complex) {
var val = (Complex(1, 0) + complex) / (Complex(1, 0) - complex);
return log(val) * Complex(1 / 2);
}