Re: Additive residual error

Hi Siwei, In a similar situation previously, I've found fixing the additive error to a small value (~= 0.0001*LOQ) has provided a work-around for this. It usually arises from a zero measurement needing to be nonzero for estimation purposes. A better fix is to use the M2 method which should lower the constraint of needing additive error. Thanks, Bill On Feb 11, 2013, at 7:27 PM, "siwei Dai" <ellen.siweidai > Hi, NM users: > > I have a typical 2-compartment model that can describe my data quite well , except the final gradient for the additive residual error is '0'. I therefore fix the additive residual error to '0', but then NM would not run. I tried different initial estimations for other parameters but the additive residual error seems to be the one that decide whether NM will run. Can anyone tell me why this would happen and how to solve it? > > Thank you very much in advance for your help. > > Siwei