[R] Pinheiro/Bates Soybean nlme failure

[Prof Brian D Ripley]

On Wed, 17 Jan 2001, Dieter Menne wrote:

> Dear Mixed Effect Friends,
>
> Somehow, R(1021, Windows) seem to run differently from S Plus:
> The soybean example from Pinheiro/Bates on page 290 fails
> in R. (Soybean1 is Soybean with the NA and "critical" case
> removed. Same procedure with full Soybean).
>
> > fm1Soy.lis<-nlsList(weight~SSlogis(Time,Asym,xmid,scal),data=Soybean1)
> > fm1Soy.nlme<-nlme(fm1Soy.lis)
> Error: Singularity in backsolve at level 0, block 1
> In addition: There were 50 or more warnings (use warnings() to see the first 50)
> > warnings()
> Warning messages:
> 1: Singular precision matrix in level -1, block 1
> 2: Singular precision matrix in level -1, block 1

It is not the only such.  nlme-3.1-x,  x >=8 has a different algorithm and
fails much more often for me than nlme-3.1-6, say.  Both fail more
often than nlme 3.3 on S-PLUS (you didn't say what you were using).

The Windows port of nlme does pass Rcmd check, so does run the examples
correctly.

-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272860 (secr)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595

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