  L. A. Bunimovich and B. Z. Webb developed a theory for transforming a finite
weighted graph while preserving its spectrum, referred as isospectral reduction
theory. In this work we extend this theory to a class of operators on Banach
spaces that include Markov type operators. We apply this theory to infinite
countable weighted graphs admitting a finite structural set to calculate the
stationary measures of a family of countable Markov chains.
