[R] How to put factor variables in an nls formula ?

From: François Morneau <francois.morneau_at_cirad.fr>
Date: Fri 19 Aug 2005 - 00:20:58 EST


Hello,

I want to fit a Gompertz model for tree diameter growth that depends on a 4 levels edaphic factor (‘Drain’) and I don’t manage to introduce the factor variable in the formula.
Dinc is the annual diameter increment and D is the Diameter.

 >treestab

 >     Dinc     D      Drain

[1,] 0.03 26.10 2
[2,] 0.04 13.05 1
[3,] 0.00 24.83 1
[4,] 0.00 15.92 4
[5,] 0.00 12.25 4
[6,] 0.00 11.78 4
[7,] 0.00 16.87 4
[8,] 0.00 15.12 4
[9,] -0.01 13.53 4
[10,] 0.04 16.55 3 [11,] 0.025 16.07 3 [12,] 0.00 30.24 3 [13,] 0.06 15.28 2

etc…
 >contrasts(Drain)<-contr.sum(4)
 >mymodel<-nls(Dinc~r*(1+Drain)*D*log(Asym/D), data=treestab, start(r=0.05, Asym=40))

Error in numericDeriv(form[[3]], names(ind), env) :

         Missing value or an infinity produced when evaluating the model In addition: Warning messages:
1: + not meaningful for factors in: Ops.factor(1, Drain) 2: + not meaningful for factors in: Ops.factor(1, Drain)

Do I need to use another function instead of nls to correctly include the factor ‘Drain’ ?

Thanks,

François



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