Reciprocal inverse Gaussian distribution

The probability density function for reciprocal inverse Gaussian distribution is:

.. math::

f(x, k) = \frac{1}{\sqrt{2\pi x}}
                \exp\left(\frac{-(1-k x)^2}{2k^2x}\right)

for a real number :math:x \ge 0.

The following plots show the pdf and cdf:

.. image:: ../../../../tests/imgs/stats/continuous/recipinvgauss/recipinvgausspdf.png :align: center :width: 480

.. image:: ../../../../tests/imgs/stats/continuous/recipinvgauss/recipinvgausscdf.png :align: center :width: 480