; docformat = 'rst' ;+ ; Inverse hyperbolic cosine. Uses the formula: ; ; $$\text{acosh}(z) = \ln(z + \sqrt{z + 1} \sqrt{z - 1})$$ ; ; :Examples: ; The arc hyperbolic sine function looks like:: ; ; IDL> x = 2.5 * findgen(1000) / 999. + 1. ; IDL> plot, x, mg_acosh(x), xstyle=1 ; ; This should look like: ; ; .. image:: acosh.png ; ; :Returns: ; float, double, complex, or double complex depending on the input ; ; :Params: ; z : in, required, type=numeric ; input ;- function mg_acosh, z compile_opt strictarr return, alog(z + sqrt(z + 1) * sqrt(z - 1)) end