Pareto/NBD parameters - a vector with r, alpha, s, and beta, in
that order. r and alpha are unobserved parameters for the NBD transaction
process. s and beta are unobserved parameters for the Pareto (exponential
gamma) dropout process.
lim
The upper-bound of the x-axis. A number is chosen by the function
if none is provided.
Value
Distribution of customers' propensities to drop out.
Details
This returns the distribution of each customer's exponential parameter that
determines their lifetime (using the Pareto/NBD assumption that a customer's
lifetime can be modeled with an exponential distribution).