Bug 16864

Summary: nlme: lme gives incorrect answers without warning with redundant data
Product: R Reporter: Jonathan Dushoff <dushoff>
Component: AnalysesAssignee: R-core <R-core>
Status: UNCONFIRMED ---    
Severity: minor    
Priority: P5    
Version: R 3.2.4   
Hardware: x86_64/x64/amd64 (64-bit)   
OS: Linux   
Attachments: nlme analysis of redundant data, with noise titrated to near zero

Description Jonathan Dushoff 2016-05-03 22:38:21 UTC
Created attachment 2072 [details]
nlme analysis of redundant data, with noise titrated to near zero

On certain pathological data sets, where the data is nearly redundant, lme returns nonsensical answers (which is understandable), but does so without producing any warnings (which is worrisome).

I would like to see warnings when I encounter singularities, so that I can be aware that results might not be reliable.

I attach a simple, complete, example. There is more discussion of the issue at https://htmlpreview.github.io/?https://github.com/dushoff/scratch/blob/master/nlme.html