# [R] Prediction plots

Boris Steipe boris.steipe at utoronto.ca
Wed Apr 19 18:20:34 CEST 2017

Can you provide a small reproducible example and explain what exactly is going wrong?

Just a handful of data points will do.

B.

> On Apr 18, 2017, at 2:16 PM, Santiago Bueno <swbueno at gmail.com> wrote:
>
> 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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>
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