[Rd] nlme: lme gives incorrect answers without warning with redundant data

[Jonathan Dushoff]

I think this issue will be of interest to the list. It seems like a
problem with nlme, and I was drawn into it because of a collaborator
who encountered this issue in a simple experiment and wound up
questioning the mixed model approach to his question.

The issue is that lme, when faced with certain numerically unstable
problems, seems to produce incorrect answers (understandable), but
without warnings (bad, in my opinion).

I have attached a reproducible example.

There is more information here:
https://htmlpreview.github.io/?https://github.com/dushoff/scratch/blob/master/nlme.html
and https://bugs.r-project.org/bugzilla3/show_bug.cgi?id=16864. The
first link shows my session information.

Jonathan