Commit 6b1c58f7 authored by Philipp Arras's avatar Philipp Arras
Browse files

Add documentation to InverseGammaModel

parent 36c7db94
......@@ -31,6 +31,27 @@ from ..sugar import makeOp
class InverseGammaModel(Operator):
def __init__(self, domain, alpha, q):
"""Model which transforms a Gaussian into an inverse gamma distribution.
The pdf of the inverse gamma distribution is defined as follows:
.. math::
\frac {\beta ^{\alpha }}{\Gamma (\alpha )}}x^{-\alpha -1}\exp \left(-{\frac {\beta }{x}}\right)
That means that for large x the pdf falls off like x^(-alpha -1).
The mean of the pdf is at q / (alpha - 1) if alpha > 1.
The mode is q / (alpha + 1).
domain : Domain, tuple of Domain or DomainTuple
The domain on which the field shall be defined. This is at the same
time the domain and the target of the operator.
alpha : float
The alpha-parameter of the inverse-gamma distribution.
q : float
The q-parameter of the inverse-gamma distribution.
self._domain = self._target = DomainTuple.make(domain)
self._alpha = alpha
self._q = q
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