Nelder-Mead Simplex Modifications for Simulation Optimization.

When the Nelder-Mead method is used to optimize the expected response of a stochastic system (e.g., an output of a discrete-event simulation model), the simplex-resizing steps of the method introduce risks of inappropriate termination. We give analytical and empirical results describing the performance of Nelder-Mead when it is applied to a response function that incorporates an additive white-noise error, and we use these results to develop new modifications of Nelder-Mead that yield improved estimates of the optimal expected response. Compared to Nelder-Mead, the best performance was obtained by a modified method, RS + S9, in which (a) the best point in the simplex is reevaluated at each shrink, step and (b) the simplex is reintroduced by 10% (rather than 50%) at each shrink step. In a suite of 18 test problems that were adapted from the MINPACK collection of NETLIB, the expected response at the estimated optimal point, at an average cost of three times as many function evaluations. Two well-known existing modifications for stochastic responses, the (n + 3)-rule and the next-to-worst rule, were found to be inferior to the new modification RS + S9. [ABSTRACT FROM AUTHOR]