Function beta for the Laplace prior
Given a value or vector x of values, find the value(s) of the function beta(x) = g(x)/phi(x) - 1 , where g is the convolution of the Laplace density with scale parameter a with with the normal density phi(x).
beta.laplace(x, a = 0.5)
the value or vector of data values
the scale parameter of the Laplace distribution
A vector the same length as x is returned, containing the value(s) beta(x).
The Laplace density is given by gamma(u)= (a/2) exp ( - a|u| ) and is also known as the double exponential density.
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