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Dear members,
I am in the process of developing a user model for capacity limited
metabolite kinetics. I am facing the following error message after
first iteration every time when I run the model.
Error: 10150 - The parameter variance-covariance matrix is singular.
Program terminated.
It would be really great if somebody can explain me the reasons for
getting this error and the ways to solve this.
One more thing is that, the weighted sum of squares for the first
iteration remained same every time even though I am changing the
initial estimates of parameters. Is it possible?
Thanks & Regards
Sivacharan Kollipara
Metabolism & Pharmacokinetics Department
Ranbaxy Research Laboratories
India
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The following message was posted to: PharmPK
Sure.
This error be a result of a problem with the data.. but usually, its
because
the nonlinear model you are using has parameters that are not
independent.
Every parameter needs freedom to minimize its objective function on
its own,
and the var-cov matrix shows the degree of interdependence, but when the
model is overparameterized there are no minimums to converge upon, so
the
program terminates.
This can usually be solved by combining two parameters (the correct ones
obviously).
Unfortunately, if you are attempting an integrated nonlinear model in
lieu
of differential expressions in the user-defined code, you run the risk
of
having a transcendental equation in lieu of an explicit one....which I
suspect could be at the root of the problem. Switch your model to
DZ(x)etc., and you should be ok.
Hope it helps.
Shawn D. Spencer, Ph.D. R.Ph.
Assistant Professor of Biopharmaceutics
Florida A&M College of Pharmacy
Tallahassee, FL 32307
shawn.spencer.-a-.famu.edu
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The following message was posted to: PharmPK
Dear Sivacharan,
it might help, if you provide us with the code of your model.
Maybe the model parameters are non-idetinfiable or you have not enough
experimental data to determine parameters uniquely along with their
variability measures.
Regards
Wojciech Jawien
Faculty of Pharmacy
Jagiellonian Univ.
Krakow, Poland
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