Half-norm distribution

The probability density function for the Half-normal distribution is:

.. math::

f(x) = \sqrt{2/\pi} \exp(-x^2 / 2)

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

.. image:: ../../../../tests/imgs/stats/continuous/halfnorm/halfnormpdf.png :align: center :width: 480

.. image:: ../../../../tests/imgs/stats/continuous/halfnorm/halfnormcdf.png :align: center :width: 480