`Controlled' versions of the Collatz-Wielandt and Donsker-Varadhan formulae

This is an overview of the work of the authors and their collaborators on the characterization of risk sensitive costs and rewards in terms of an abstract Collatz-Wielandt formula and in case of rewards, also a controlled version of the Donsker-Varadhan formula. For the finite state and action case, this leads to useful linear and dynamic programming formulations in the reducible case.