BG/NBD parameters - a vector with r, alpha, a, and b, in that
order. r and alpha are unobserved parameters for the NBD transaction
process. a and b are unobserved parameters for the Beta geometric dropout
process.
lim
upper-bound of the x-axis. A number is chosen by the function if
none is provided.
Value
Distribution of customers' propensities to purchase.
Details
This returns the distribution of each customer's Poisson parameter, which
determines the rate at which each customer buys.