Re: [R] Problems with nlme: Quinidine example

From: Dieter Menne <dieter.menne_at_menne-biomed.de>
Date: Fri 08 Jul 2005 - 19:03:20 EST

 <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
(2000).
>
> 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



R-help@stat.math.ethz.ch mailing list
https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html Received on Fri Jul 08 19:08:56 2005

This archive was generated by hypermail 2.1.8 : Fri 03 Mar 2006 - 03:33:22 EST