Johnson Unbounded Distribution (JohnsonSU)

The density function of the Johnson unbounded distribution (JohnsonSU) is

\[  f(x) = \frac{\delta }{\lambda \sqrt {2\pi }}g’\left(\frac{x - \xi }{\lambda }\right)\mbox{exp}\left(-\frac{1}{2}\left[\gamma + \delta g\left(\frac{x - \xi }{\lambda }\right)\right]^2\right)  \]

where

\[  \begin{array}{l} g(y) = \mbox{ln}\left[y + \sqrt {y^2 + 1}\right]\\ g’(y) = \frac{1}{\sqrt {y^2 + 1}} \end{array}  \]

and $x \in (-\infty , \infty )$.

Parameters:

$\delta $ (delta)

is a shape parameter, $\delta > 0$.

$\gamma $ (gamma)

is a shape parameter.

$\xi $ (xi)

is the location parameter.

$\lambda $ (lambda)

is the scale parameter, $\lambda > 0$.