Published online by Cambridge University Press: 01 July 2016
Let (φ(X n ))n be a function of a finite-state Markov chain (X n )n . In this article, we investigate the conditions under which the random variables φ(n ) have the same distribution as Y n (for every n), where (Y n )n is a Markov chain with fixed transition probability matrix. In other words, for a deterministic function φ, we investigate the conditions under which (X n )n is weakly lumpable for the state vector. We show that the set of all probability distributions of X 0, such that (X n )n is weakly lumpable for the state vector, can be finitely generated. The connections between our definition of lumpability and the usual one (i.e. as the proportional dynamics property) are discussed.