Dear all,

I am using the nlme package to find the best model using non-linear  
mixed effects model.

After the all the other things needed, I did

 >  M1<- nlme(NShrubs~A*exp(-B*CED),data=DataSg,fixed=list 
(A~SITE,B~1), random=B~1,start=list(fixed=c 
(1.66,1.66,1.66,1.66,1.66,1.66,1.66,1.66,0.0038)),control=lmc)

and it was ok.


However, the data showed to need random parameters at both the  
intercept and the slope.
And I can not understand why do I always get an error message like:

Error in parse(text = paste("~", paste(nVal, collapse = "/"))) :
   unexpected end of input in "~ "
or
Error in nlme.formula(NShrubs ~ A * exp(-B * CED), data = DataSg,  
fixed = list(A ~  :
   random formula must be a formula or list of formulae


Could you please tell me where/what am I doing wrong (in any of the  
following options I have uses)?


 >  M1<- nlme(NShrubs~A*exp(-B*CED),data=DataSg,fixed=list 
(A~SITE,B~1), random=list(B~1),start=list(fixed=c 
(1.66,1.66,1.66,1.66,1.66,1.66,1.66,1.66,0.0038)),control=lmc)

 > M1<- nlme(NShrubs~A*exp(-B*CED),data=DataSg,fixed=list 
(A~SITE,B~1), random=list(B~1(SITE)),start=list(fixed=c 
(1.66,1.66,1.66,1.66,1.66,1.66,1.66,1.66,0.0038)),control=lmc)

 > M1<- nlme(NShrubs~A*exp(-B*CED),data=DataSg,fixed=list 
(A~SITE,B~1), random=~CED,start=list(fixed=c 
(1.66,1.66,1.66,1.66,1.66,1.66,1.66,1.66,0.0038)),control=lmc)

 > M1<- nlme(NShrubs~A*exp(-B*CED),data=DataSg,fixed=list 
(A~SITE,B~1), random=list(A~I,B~I),start=list(fixed=c 
(1.66,1.66,1.66,1.66,1.66,1.66,1.66,1.66,0.0038)),control=lmc)

 > M1<- nlme(NShrubs~A*exp(-B*CED),data=DataSg,fixed=list 
(A~SITE,B~1), random=~1,start=list(fixed=c 
(1.66,1.66,1.66,1.66,1.66,1.66,1.66,1.66,0.0038)),control=lmc)

 > M1<- nlme(NShrubs~A*exp(-B*CED),data=DataSg,fixed=list 
(A~SITE,B~1), random=~1|SITE,start=list(fixed=c 
(1.66,1.66,1.66,1.66,1.66,1.66,1.66,1.66,0.0038)),control=lmc)

 > M1<- nlme(NShrubs~A*exp(-B*CED),data=DataSg,fixed=list 
(A~SITE,B~1), random=~1|SITE/T,start=list(fixed=c 
(1.66,1.66,1.66,1.66,1.66,1.66,1.66,1.66,0.0038)),control=lmc)


I would be really greatful if you can please help me on this.


Best regards,

Sara Maltez Mouro

Centro de Ecologia Funcional
Departamento de Botânica
Universidade de Coimbra

sara@gmesintra.com
www.uc.pt/ecology/saramaltezmouro


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