[R] Problems with nlme: Quinidine example
dieter.menne at menne-biomed.de
Fri Jul 8 11:03:20 CEST 2005
<rich <at> mi.fu-berlin.de> writes:
> This concerns the "Clinical Study of Quinidine" example on page 380
> of the book "Mixed-Effects Models in S and S-PLUS" by Pinheiro and Bates
> I have tried to reproduce the example, but get an error:
> system is computationally singular: reciprocal condition number =
In R, the underlying non-linear solver is different from that used in S. In
general, I found the S-version converged in more cases than the R-version, but
the opposite may also be true.
Sometimes it helps to fiddle with the control parameters on nlme, for example I
got around some ping-ponging by setting pnlsTol to a large value, but check the
sanity of your results. Looks like this will not help in this case, as in
library\nlme\scripts\ch08.R Douglas Bates has added the following:
## This fit just ping-pongs.
# nlme(conc ~ quinModel(Subject, time, conc, dose, interval,
# lV, lKa, lCl),
The master has spoken, no chance. It's a good idea to check these files if an
example from the book does not work.
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