Johnson SB distribution

The probability density function for the Johnson SB distribution is:

.. math::

f(x, a, b) = \frac{b}{x(1-x)}  \phi(a + b \log \frac{x}{1-x} )

where :math:b > 0,x \in [0,1], :math:\phi is the pdf of the normal distribution. The following plots show the pdf and cdf:

.. image:: ../../../../tests/imgs/stats/continuous/johnsonsb/johnsonsbpdf.png :align: center :width: 480

.. image:: ../../../../tests/imgs/stats/continuous/johnsonsb/johnsonsbcdf.png :align: center :width: 480