Uses MBG/CNBD-k model parameters to return the probability distribution of purchase frequencies for a random customer in a given time period, i.e. P(X(t)=x|r,alpha,a,b)
mbgcnbd.Px(params, t, x)MBG/CNBD-k parameters - a vector with 'k', r, alpha, a and b
in that order.
length of time for which we are calculating the expected number of transactions.
number of transactions for which probability is calculated.
P(X(t)=x|r,alpha,a,b). If any of the input parameters has a length greater than 1, this will be a vector of expected number of transactions.