RE: Describing variability

From: "Kowalski, Ken" Subject:RE: [NMusers] Describing variability Date:Wed, 2 Apr 2003 13:39:49 -0500 Bill, I would very much like to see a concrete example where you claim that NONMEM will converge with a failed $COV step but the model is not ill-conditioned. I'm willing to accept that such a situation can arise. Perhaps it is related to numerical deficiencies with NONMEM's optimization algorithm and mathematical operations (basically what Steve Duffull was saying about matrices that MATLAB had no problems inverting but NONMEM did). Still, my own experience with failed $COV steps are that they are usually related to ill-conditioning and not numerical problems with the mathematical calculations. Regards, Ken ps Is this fun or what? :-)