; docformat = 'rst' ;+ ; Inverse hyperbolic tangent. Uses the formula: ; ; $$\text{atanh}(z) = \frac{\ln(\frac{1 + z}{1 - z})}{2}$$ ; ; :Examples: ; The arc hyperbolic sine function looks like:: ; ; IDL> x = 2. * findgen(1000) / 999. - 1. ; IDL> plot, x, mg_atanh(x), xstyle=1 ; ; This should look like: ; ; .. image:: atanh.png ; ; :Returns: ; float, double, complex, or double complex depending on the input ; ; :Params: ; z : in, required, type=numeric ; input ;- function mg_atanh, z compile_opt strictarr return, alog((1 + z) / (1 - z)) / 2.0 end