An ergodic Markov chain is started in equilibrium (i.e., with initial probability vector w). The mean time until the next occurrence of state si is \bar{m}_i= \sum\limits_{k} w_k m_{ki}+ w_i r _i. Show that \bar{m}_i= zii/wi, by using the facts that wZ = w and mki =(zii − zki)/wi.
We know that wZ = w. We also know that mki = (zii − zki)/wi and wi = 1/ri. Putting these in the relation
\bar{m}_i= \sum \limits_k w_km_{ki}+ w_ir_iwe see that
\bar{m}_i= \sum \limits_k w_k\frac{z_{ii}-z_{ki}}{w_i}+1 \\= \frac{z_{ii}}{w_i}\sum\limits_{k}{w_k}-\frac{1}{w_i}\sum\limits_{k}{w_k z_{ki}}+1 \\= \frac{z_{ii}}{w_i}-1+1 = \frac{z_{ii}}{w_i}.