Consistent Approximations for Optimal Control Problems Based on Runge--Kutta Integration

  • Authors:
  • A. Schwartz;E. Polak

  • Affiliations:
  • -;-

  • Venue:
  • SIAM Journal on Control and Optimization
  • Year:
  • 1996

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Abstract

This paper explores the use of Runge--Kutta integration methods in the construction of families of finite-dimensional, consistent approximations to nonsmooth, control and state constrained optimal control problems. Consistency is defined in terms of epiconvergence of the approximating problems and hypoconvergence of their optimality functions. A significant consequence of this concept of consistency is that stationary points and global solutions of the approximating discrete-time optimal control problems can only converge to stationary points and global solutions of the original optimal control problem. The construction of consistent approximations requires the introduction of appropriate finite-dimensional subspaces of the space of controls and the extension of the standard Runge--Kutta methods to piecewise-continuous functions.It is shown that in solving discrete-time optimal control problems that result from Runge--Kutta integration, a non-Euclidean inner product and norm must be used on the control space to avoid potentially serious ill-conditioning effects.