Returns m=length(ts) probabilities, where the j-th probability is the
probability that the j-th component will be in the candidate set.
probabilities are a function of rank (rather than by component failure
times).
Details
The shape of the masking is given by two parametrs, alpha, which must be
non-negative, and beta, which must be between 0 and 1.
As alpha goes to 0, the probability vector approaches
(beta, beta, ..., 1, beta, ..., beta)
where the 1 is for the failed component and as alpha goes to infinity, it
assigns probability 1 and beta respectively to rank 1 (failed component)
and rank 2 components (and the remaining probabilities are zero).