[R] Package nlme

[John Fox]

Dear Rohan,

Bert Gunter has already made several general useful suggestions.

In addition, why did you make the variable on the left-hand side of the 
model a factor? Shouldn't it be a numeric variable?

I hope this helps,
  John

-- 
John Fox, Professor Emeritus
McMaster University
Hamilton, Ontarion, Canada
web: https://socialsciences.mcmaster.ca/jfox/

On 4/7/2022 6:30 AM, Rohan Richard via R-help wrote:
> Dear Help Desk,
> 
> I am trying to perform a non-linear regression (Sigmoid curves) using the R package nlme. My field trial is a randomised complete block design (RCBD) with 3 blocks and I would like to assess the block effect in the model. Do you know how I can incorporate the block term in nlme function?
> 
> So far I tried the following code and it did not work and I an error error message:
> 
> # code
> minitab$NDVI<-as.factor(minitab$NDVI)
> modnlme1 <- nlme(NDVI ~ a + d / (1 + exp(-b * (DegreeDay - m)) ), data = minitab,
>                   random =a + d + b + m~ 1|Block,
>                   fixed = list(a ~ Lines1, d~Lines1,b ~ Lines1, m ~ Lines1),
>                   weights = varPower(),
>                   start=c(b=0.5,c=3,d=0.4, e=700), control = list(msMaxIter = 200))
> 
> #Error message
> Error in `contrasts<-`(`*tmp*`, value = contr.funs[1 + isOF[nn]]) :
>    contrasts can be applied only to factors with 2 or more levels
> 
> Could you please kindly help me?
> 
> Thank you in advance,
> 
> Best wishes,
> 
> Rohan
> 
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