[R] Problems with nlme: Quinidine example

Dieter Menne 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 =
> 6.61723e-17

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.
#fm1Quin.nlme <-
#  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.

Dieter Menne

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