Lag Time Problem

From: peter.bonate@quintiles.com Subject: Lag Time Problem Date: Wed, 4 Apr 2001 12:04:19 -0500 I am having a problem with ADVAN4 TRANS4. I am running a 2-compartment model with proportional error model. Up to this point, everything has been running smooth. When I add a lagtime (ALAG1) to the model, I get the following error message: MONITORING OF SEARCH: 0PROGRAM TERMINATED BY OBJ ERROR IN CELS WITH INDIVIDUAL 1 ID= .10000000E+01 WEIGHTED SUM OF "SQUARED" INDIVIDUAL RESIDUALS IS INFINITE MESSAGE ISSUED FROM ESTIMATION STEP AT 0TH ITERATION, UPON EVALUATION OF GRADIENT So what I did next was to add an additive error term to make an additive and proportional error model. The model converges with a decrease in the objective function of 13 points, but with R-matrix singularity - the additive EPS(2) term is 1E-13. So next I tried fixing the EPS(2) term to a very small value, 0.0001. I still get R-matrix singularity. Can anyone suggest something here. Thanks. Peter Bonate

From: "Gibiansky, Ekaterina" <gibianskye@globomax.com> Subject: RE: Lag Time Problem Date: Wed, 4 Apr 2001 13:24:35 -0400 Peter, did you try to make an initial value for LAG smaller than the time of first observed non-zero concentration? It may help at 0 iteration, though this error can re-appear later. If it does, ETA for lag may help, though it is a shaky thing Katya ________________________ Ekaterina Gibiansky, PhD Senior Scientist GloboMax LLC 7250 Parkway Drive, Suite 430 Hanover, MD 21076 Voice (410) 782-2234 FAX (410) 712-0737 E-mail: gibianskye@globomax.com