RE: use of REPEAT option

Hi Pharavee, The REPEAT option on the $ESTIMATION record causes the following: 1) the matrix that is used to guide the parameter search is rescaled using the final estimates from the first search and 2) a new parameter search is conducted starting with the previous parameter estimates and the rescaled matrix. The idea was that if the first search yielded a local minimum then the second search might find a lower minimum. However, experience demonstrated that the repeated search usually failed to move from the original minimum even if the original was a local minimum. Consequently, the option has received very little attention or use. A commonly used strategy to try to defend against a local minimum is to use multiple runs of the same model but with different sets of initial estimates. If one can obtain the same minimum objective function value for several of these runs then this result is taken as supporting evidence that this objective function value could be, but not guaranteed to be, a global minimum. See section I.36 of NONMEM USERS GUIDE INTRODUCTION TO NONMEM 7.2.0 (nm720.pdf) for implementation of this latter approach. Tom