Kelly's lemma
In probability theory, Kelly's lemma states that for a stationary continuous-time Markov chain, a process defined as the time-reversed process has the same stationary distribution as the forward-time process.[1] The theorem is named after Frank Kelly.[2][3][4][5]
Statement
For a continuous time Markov chain with state space S and transition-rate matrix Q (with elements qij) if we can find a set of non-negative numbers q'ij and a positive measure π that satisfy the following conditions:[1]
then q'ij are the rates for the reversed process and π is proportional to the stationary distribution for both processes.
Proof
Given the assumptions made on the qij and π we have
so the
global balance equations
are satisfied and the measure π is proportional to the stationary distribution of the original process.
By symmetry, the same argument shows that π is also proportional to the stationary distribution of the reversed process.
References
- ^ ISBN 144196472X.
- ISBN 0471276014.
- ISBN 013474487X.
- JSTOR 1425912.
- ISBN 978-0-387-00211-8.