An Accelerator for Packages Solving Discrete-Time Optimal Control Problems

We present an accelerator scheme for use with existing packages that solve nonlinear programming problems with a large number of inequality constraints that arise in the process of discretizing continuous-time optimal control problems with state-space constraints. This scheme is based on the concept of outer approximations used in semi-infinite programming and acts as an external, active constraints set strategy. Our scheme constructs a finite sequence of inequality constrained nonlinear programming problems, containing a progressively larger subset of the constraints in the original problem, and submits these problems to a nonlinear programming solver for a fixed number of iterations. We prove that this scheme computes a solution of the original problem and show, by means of numerical experiments, that it results in reductions in computing time ranging from a factor of 6 to a factor of over 400.