Greedy Expected Posterior Loss // Summarises a collection of
partitions into a single optimal partition. The objective
function is the expected posterior loss, and the minimisation
is performed through a greedy algorithm described in Rastelli,
R. and Friel, N. (2017) "Optimal Bayesian estimators for latent
variable cluster models" DOI:10.1007/s11222-017-9786-y.