FO vs FOCE vs LAPLACIAN

From: "Rajanikanth Madabushi" <rajanim@ufl.edu> Subject:[NMusers] FO vs FOCE vs LAPLACIAN Date: Tue, 15 Jul 2003 19:28:12 -0400 Hi all, I have sparse PK data( two points per individual) following i.v bolus admnistration of a drug known to follow two compartment model. I am using ADVAN3 TRANS4 subroutine. When i use FO method, the minimization is terminated and the following error message appears MINIMIZATION TERMINATED DUE TO PROXIMITY OF NEXT ITERATION EST. TO A VALUE AT WHICH THE OBJ. FUNC. IS INFINITE AT THE LAST COMPUTED INFINITE VALUE OF THE OBJ. FUNCT.: PRED EXIT CODE = 1 When FOCE method is used, minimization is successful. When the LAPLACIAN method is used,minimization is successful but MINIMIZATION SUCCESSFUL R MATRIX ALGORITHMICALLY SINGULAR AND ALGORITHMICALLY NON-POSITIVE-SEMIDEFINITE COVARIANCE STEP ABORTED Is it not usually considered that FO method is suitable for a sparse data situation while FOCE for a rich data situation? My question is why did FO method not converge successfully when FOCE and LAPLACIAN methods gives successful minimization? The other question was in the event of successful minimization obtained for all the three of the above methods but if the parameter estimates for the parameters are quite different, which method of estimation be adopted?? Thanking in advance. Raj Rajanikanth Madabushi Post Doc Assoc Department of Pharmaceutics University of Florida Gainesville, FL 32610