Methods for solving Hamilton-Jacobi-Bellman equations

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2019-06-21

Authors

Martin, Lindsay Joan

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Abstract

The goal of this thesis is to present two frameworks for the computation of the solutions of Hamilton-Jacobi-Bellman (HJB) equations. In Chapter 2, we present a framework for computing solutions to HJB equations on smooth hypersurfaces. It is well known that the viscosity solution of the HJB equation is equivalent to the value function of a corresponding optimal control problem. We extend the optimal control problem given on the surface to an equivalent one defined in a sufficiently thin narrow band of surface. The extension is done appropriately so that the viscosity solution of the extended HJB equation in the narrow band is identical to the constant normal extension of the viscosity solution of the HJB equation on the surface. With this framework, we can easily use efficient, existing (high order) numerical methods developed on Cartesian grids to solve HJB equations on surfaces, with a computational cost that scales with the dimension of the surfaces. This framework also provides a systematic way for solving HJB equations on unstructured point clouds that are sampled from a surface. In Chapter 3, we present a parallelizable domain decomposition algorithm to solve Eikonal equations, a special case of HJB equations. The method is an iterative two-scale method that uses a parareal-like update scheme in combination with standard Eikonal solvers. The purpose of the two scales is to accelerate convergence and maintain accuracy. We adapt a weighted version of the parareal method for stability, and the optimal weights are studied via a model problem. One can view the new method as a general framework where an effective coarse grid solver is computed “on the fly” from coarse and fine grid solutions that are computed in previous iterations. To demonstrate the framework, we develop a specific scheme using Cartesian grids and the fast sweeping method for solving Eikonal equations. Numerical examples are given to demonstrate the method’s effectiveness on a variety of stereotypes of Eikonal equations.

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