How do I write this nonlinear regression

Asked Sep 20 '18 at 19:40

Active Sep 20 '18 at 19:42

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what is the correct way of writing this nonlinear regression equation in r

a0*(D^a1)*(H^a2)X^(b1(Z^4)+b2*(1/exp(D/H)+b3*(X^0.1)+b4*(1/D)+b5*(H^Q)+b6*X)

I tried writing it with the format below but r said I should remove the comma sign(,) between the formula and data. I tried removing the comma sign, still I was unable to run the data.

My data is in table format with D,H,Z,X,Q variables. and a0,a1,a2,b1,b2,b3,b4,b5,b6 are all parameters to be estimated.

model2 <- nls (Dbh ~ a0*(Dbh^a1)*(Tht^a2)*X^(b1*(Z^4)+b2*((1/exp)^(Dbh/Tht))+b3*(X^0.1)+b4*(1/Dbh)+b5*(Tht^Q)+b6*X)),  
               data = kodat,   
               Start = list(a0= 4.6, a1= 6.9, a2= 5.9, b1= 30, b2= 2.1, b3= 7.8, b4= 1.2, b5= 0.2, b6= 8.1)
summary(model2)

edited Sep 20 '18 at 19:42

user20650

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asked Sep 20 '18 at 19:40

T.awesome

1

you have an extra closing bracket somewhere... – user20650 Sep 20 '18 at 19:43
2

I also expect confusion because you use `Dbh` as the left-hand side of the formula and in the right-hand side. With the formula as you have written, `a0 = 1, a1 = 1, b* = 0` will give a perfect fit by simplifying to `Dbh = Dbh`. – Gregor Thomas Sep 20 '18 at 19:45
additionally, exp is use like `exp(Dbh/Tht)` – user20650 Sep 20 '18 at 19:47

How do I write this nonlinear regression

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