Optimal policies with heterogeneous agents: Truncation and transitions

We compare two approaches in their ability to solve for optimal Ramsey policies in heterogeneous-agent models, considering the optimal provision of a public good. First, the “transition” approach makes the problem tractable by assuming a constant path for the planner's instruments. Second, the “truncation” approach uses a Lagrangian technique, solving the Ramsey problem of a finite state space model that approximates the full model. The truncation approach is shown to compute quantitatively accurate estimates of the actual values of the planner's instruments, whereas a time-inconsistency issue is found to affect the transition approach.