Definition (Detailed balance)
A transition matrix and a pmf are said to be in detailed balance if
Theorem (Sufficient Condition for Identifying Invariant Distribution)
If and are in detailed balance, then is invariant in .
Remark
To find an invariant distribution, we could try to solve
Remark
Detailed balance is a sufficient condition for identifying invariant distribution, not a necessary one. Hence, there may be an invariant distribution but detailed balance does not guarantee finding it.
Definition (Detailed balance — continuous)
A Q-Matrix and a distribution are said to be in detailed balance if for all .
Theorem
If and are in detailed balance then .