The notation emphasizes that in general the transition probabilities are functions not only of the initial and final states, but also of the time of transition as well. When the one-step transition probabilities are independent of the time variable n, we say that the Markov chain has stationary transition probabilities. Since the vast majority of Markov chains that we shall encounter have stationary transition probabilities, we limit our discussion to this case. The Pij=Pij is independent of n, and Pij is the conditional probability that the state value undergoes a transition from I to j in one trial. It is customary to arrange these numbers Pij in a matrix, in the infinite square array