On the Convergence of Overlapping Schwarz Decomposition for Nonlinear Optimal Control

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Main Authors: Na, Sen, Shin, Sungho, Anitescu, Mihai, Zavala, Victor M.
Format: Preprint
Published: 2020
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author Na, Sen
Shin, Sungho
Anitescu, Mihai
Zavala, Victor M.
author_facet Na, Sen
Shin, Sungho
Anitescu, Mihai
Zavala, Victor M.
contents We study the convergence properties of an overlapping Schwarz decomposition algorithm for solving nonlinear optimal control problems (OCPs). The algorithm decomposes the time domain into a set of overlapping subdomains, and solves all subproblems defined over subdomains in parallel. The convergence is attained by updating primal-dual information at the boundaries of overlapping subdomains. We show that the algorithm exhibits local linear convergence, and that the convergence rate improves exponentially with the overlap size. We also establish global convergence results for a general quadratic programming, which enables the application of the Schwarz scheme inside second-order optimization algorithms (e.g., sequential quadratic programming). The theoretical foundation of our convergence analysis is a sensitivity result of nonlinear OCPs, which we call "exponential decay of sensitivity" (EDS). Intuitively, EDS states that the impact of perturbations at domain boundaries (i.e. initial and terminal time) on the solution decays exponentially as one moves into the domain. Here, we expand a previous analysis available in the literature by showing that EDS holds for both primal and dual solutions of nonlinear OCPs, under uniform second-order sufficient condition, controllability condition, and boundedness condition. We conduct experiments with a quadrotor motion planning problem and a PDE control problem to validate our theory; and show that the approach is significantly more efficient than ADMM and as efficient as the centralized solver Ipopt.
format Preprint
id arxiv_https___arxiv_org_abs_2005_06674
institution arXiv
publishDate 2020
record_format arxiv
spellingShingle On the Convergence of Overlapping Schwarz Decomposition for Nonlinear Optimal Control
Na, Sen
Shin, Sungho
Anitescu, Mihai
Zavala, Victor M.
Optimization and Control
Machine Learning
Dynamical Systems
We study the convergence properties of an overlapping Schwarz decomposition algorithm for solving nonlinear optimal control problems (OCPs). The algorithm decomposes the time domain into a set of overlapping subdomains, and solves all subproblems defined over subdomains in parallel. The convergence is attained by updating primal-dual information at the boundaries of overlapping subdomains. We show that the algorithm exhibits local linear convergence, and that the convergence rate improves exponentially with the overlap size. We also establish global convergence results for a general quadratic programming, which enables the application of the Schwarz scheme inside second-order optimization algorithms (e.g., sequential quadratic programming). The theoretical foundation of our convergence analysis is a sensitivity result of nonlinear OCPs, which we call "exponential decay of sensitivity" (EDS). Intuitively, EDS states that the impact of perturbations at domain boundaries (i.e. initial and terminal time) on the solution decays exponentially as one moves into the domain. Here, we expand a previous analysis available in the literature by showing that EDS holds for both primal and dual solutions of nonlinear OCPs, under uniform second-order sufficient condition, controllability condition, and boundedness condition. We conduct experiments with a quadrotor motion planning problem and a PDE control problem to validate our theory; and show that the approach is significantly more efficient than ADMM and as efficient as the centralized solver Ipopt.
title On the Convergence of Overlapping Schwarz Decomposition for Nonlinear Optimal Control
topic Optimization and Control
Machine Learning
Dynamical Systems
url https://arxiv.org/abs/2005.06674