fitting "power model" in nls()
Is that really the model we want? When we have problems sometimes its just a sign that the model is not very good in the first place. plot(richness ~ area) shows most of the points crowded the left and just a few points out to the right. This does not seem like a very good pattern for model fitting. plot(richness ~ log(area)) plot(log(richness) ~ log(area)) both look nicer.
On Dec 2, 2007 2:08 PM, Milton Cezar Ribeiro <milton_ruser at yahoo.com.br> wrote:
Dear all,
I am still fighting against my "power model".
I tryed several times to use nls() but I can?t run it.
I am sending my variables and also the model which I would like to fit.
As you can see, this "power model" is not the best model to be fit, but I really need also to fit it.
The model which I would like to fit is Richness = B*(Area^A)
richness<-c(44,36,31,39,38,26,37,33,34,48,25,22,44,5,9,13,17,15,21,10,16,22,13,20,9,15,14,21,23,23,32,29,20,
26,31,4,20,25,24,32,23,33,34,23,28,30,10,29,40,10,8,12,13,14,56,47,44,37,27,17,32,31,26,23,31,34,
37,32,26,37,28,38,35,27,34,35,32,27,22,23,13,28,13,22,45,33,46,37,21,28,38,21,18,21,18,24,18,23,22,
38,40,52,31,38,15,21)
area<-c(26.22,20.45,128.68,117.24,19.61,295.21,31.83,30.36,13.57,60.47,205.30,40.21,
7.99,1.18,5.40,13.37,4.51,36.61,7.56,10.30,7.29,9.54,6.93,12.60,
2.43,18.89,15.03,14.49,28.46,36.03,38.52,45.16,58.27,67.13,92.33,1.17,
29.52,84.38,87.57,109.08,72.28,66.15,142.27,76.41,105.76,73.47,1.71,305.75,
325.78,3.71,6.48,19.26,3.69,6.27,1689.67,95.23,13.47,8.60,96.00,436.97,
472.78,441.01,467.24,1169.11,1309.10,1905.16,135.92,438.25,526.68,88.88,31.43,21.22,
640.88,14.09,28.91,103.38,178.99,120.76,161.15,137.38,158.31,179.36,214.36,187.05,
140.92,258.42,85.86,47.70,44.09,18.04,127.84,1694.32,34.27,75.19,54.39,79.88,
63.84,82.24,88.23,202.66,148.93,641.76,20.45,145.31,27.52,30.70)
plot(richness~area)
I tryed to fit the following model:
m1<-nls(richness ~ Const+B*(area^A))
Thanks a lot,
miltinho
Brazil.
para armazenamento!
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