Blurb::
Aleatory uncertain variable - gamma
Description::
The gamma distribution is sometimes used to model time to complete a task, such as a repair or service task. It is a very flexible distribution with its shape governed by alpha and beta.

The density function for the gamma distribution is given by:

.. math::  f(x) = \frac{ {x}^{\alpha-1} \exp \left( \frac{-x}{\beta} \right) }
                { \beta^{\alpha}\Gamma(\alpha) },

where :math:`\mu = \alpha\beta,`  and :math:`\sigma^2 = \alpha\beta^2` .
Note that the exponential distribution is a special
case of this distribution for parameter :math:`\alpha = 1` .

Topics::
continuous_variables, aleatory_uncertain_variables

Examples::

Theory::
When used with some methods such as design of experiments and
multidimensional parameter studies, distribution bounds are inferred
to be [0, :math:`\mu + 3 \sigma` ].

For some methods, including vector and centered parameter studies, an
initial point is needed for the uncertain variables. When not given
explicitly, these variables are initialized to their means.
Faq::

See_Also::
