This function generates a configuration object for a Shifted Poisson prior on the number
of mixture components such that
$$q_M(m)= Pr (M=m)= \frac{e^{-\Lambda}\Lambda^{m-1} }{(m-1)!} , \quad m=1,2,3,\ldots$$
The hyperparameter \(\Lambda\) can either be fixed using Lambda
or assigned a \(Gamma(a,b)\) prior distribution with a
and b
.
In AntMAN we assume the following parametrization of the Gamma density:
$$p(x\mid a,b )= \frac{b^a x^{a-1}}{\Gamma(a)} \exp\{ -bx \}, \quad x>0.$$