Re: [R] Problems with nlme: Quinidine example

From: Dieter Menne <>
Date: Fri 08 Jul 2005 - 19:03:20 EST

 <rich <at>> 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 mailing list PLEASE do read the posting guide! Received on Fri Jul 08 19:08:56 2005

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