Re: [R] Fit non-lineair 3D Data

From: Antonio, Fabio Di Narzo <antonio.fabio_at_gmail.com>
Date: Mon 19 Dec 2005 - 21:50:54 EST

2005/12/18, Bart Joosen <bartjoosen@hotmail.com>:
> Hi,
>
> I have a problem with fitting a model:
> I made a dataframe with this data:
> a <- 1:3
> b <- 1:3
> c <- c(3, 2, 3, 2, 1, 2, 3, 2, 3)
> df <- expand.grid(a,b)
> df$result <- c
> names(df) <- c("A","B", "result")
>
> Although I can make a graph of the data:
> require(lattice)
> wireframe(result~A*B, data=df)
>
> I can't get a model to fit this 3D data.
>
>
> I have tried the lm function, but its easy to see that this a non lineair
> data set. The use of poly also isn't a solution.
> I tried to use nls, but there seems to be an error?
> mod <- nls(result~A:B, df, start = list (A=0, B=0))
> Error in qr.qty(QR, resid) : 'qr' and 'y' must have the same number of
> rows

That's not the proper way to use 'nls'. You have to already know which model to fit to data. 'nls' doesn't magically find it for you.

Watch at: "An Introduction to R"->"Statistical Models in R"-> "Nonlinear least squares and maximum likelihood models" for an overview.

There are various functions in R packages to do nonparametric even nonlinear fitting. Anyway, you should keep in mind that you really have'nt a lot of observations, so parametric models should be more appropriate.

Antonio, Fabio Di Narzo.

>
> Is there a way to fit this data?
>
>
> Thanks for your time by reading this, hopefully I will get an answer.
>
> Bart Joosen
>
> [[alternative HTML version deleted]]
>
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R-help@stat.math.ethz.ch mailing list
https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html Received on Mon Dec 19 21:57:36 2005

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