I am having difficulty understanding the syntax of the nlme() function for
nonlinear mixed models.  The data frame is called Marouane.chlorophyll.  The
model involves a dependent variable (Absorb) and an independent variable
(Ch.surf), which are both numeric variables in the data frame.  The data are
hierarchically grouped as Espece, Plante nested within Espece, and Feuille
nested within Plante (i.e. leaves within plants within species).  Espece is
defined as a factor and Plante and Feuille are defined as numeric in the
data frame.  There are two parameters (k1 and b) and I want to fit a model
in which these two parameters vary randomly across Espece and Plante (with
Feuille being the residual level).  Here is how I have specified the call to
nlme:
 
> fit<-nlme(model=Absorb~ k1 - (1/(b*Ch.surf)),
+ data=Marouane.chlorophyll,fixed=k1+b~1,
+ groups=~Espece/Plante,
+ start=list(k1=97.8, b=4.68))
 
However, there is something wrong with this syntax because I get the
following error:
 
Problem in names<-: Invalid length for names attribute: structu
re(.Data = list(structure(.Data = numeric(0), class .... 
 
Can someone explain what I am doing wrong?

 

Bill Shipley

North American Editor, Annals of Botany

Editor, "Population and Community Biology" series, Springer Publishing

Département de biologie, Université de Sherbrooke,

Sherbrooke (Québec) J1K 2R1 CANADA

Bill.Shipley@USherbrooke.ca

http://callisto.si.usherb.ca:8080/bshipley/

 

 

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