[R] Prediction plots

[Santiago Bueno]

Thanks Boris, the following is an extract of my data. I have developed
biomass models using codes like:

start <- coef (lm(log(Btot)~I(log(dbh**2*haut)),data=dat[dat$Btot>0,]))

start[1] <- exp(start[1])

names(start) <- c("a","b")

M1 <- nls(Btot~a*(dbh**2*haut)**b,data=dat,start=start,weights=1/dat$dbh**4)


start <- coef(lm(log(Btot)~I(log(dbh))+I(log(haut)),data=dat[dat$Btot>0,]))

start[1] <- exp(start[1])

names(start) <- c("a","b1","b2")

M2 <- nls(Btot~a*dbh**b1*haut**b2,data=dat,start=start,weights=1/dat$dbh**4)


Tree No dbh haut Btot
1 35.00 18.90 0.535
2 25.00 16.60 0.248
3 23.00 19.50 0.228
4 13.50 15.60 0.080
5 20.00 18.80 0.172
6 23.00 17.40 0.190
7 29.00 19.90 0.559
8 17.60 18.20 0.117
9 31.00 25.30 0.645
10 26.00 23.50 0.394
11 13.00 13.00 0.038
12 32.00 20.70 0.443
It is my interest to get prediction plots for the models. I have tried to
use the following codes with no success: Let m be one of the fitted models
with dbh as the only entry. To construct a plot of the predictions made by
this model I have tried:
with(dat,plot(dbh,Btot,xlab="Dbh(cm)",ylab="Biomass (t)"))
D <- seq(par("usr")[1],par("usr")[2],length=200)
lines(D,predict(m,newdata=data.frame(dbh=D)),col="red")
For a model m that has dbh and height as entries, I have tried to get its
predictions as follows:
D <- seq(0,180,length=20)
H <- seq(0,61,length=20)
B <- matrix(predict(m,newdata=expand.grid(dbh=D,height=H)),length(D))

Can someone provide help please!!!


Best regards,

Santiago Bueno

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