Inverted Gamma distribution

The probability density function for the inverted gamma distribution is:

.. math::

f(x, k) = \frac{x^{-k-1}}{\Gamma(k)} \exp(-\frac{1}{x})

where :math:x \ge 0, k > 0. The following plots show the pdf and cdf:

.. image:: ../../../../tests/imgs/stats/continuous/invgamma/invgammapdf.png :align: center :width: 480

.. image:: ../../../../tests/imgs/stats/continuous/invgamma/invgammacdf.png :align: center :width: 480