Re: [R] Polynomial fitting

From: <apjaworski_at_mmm.com>
Date: Mon, 7 Jan 2008 11:27:02 -0600


Jonas,

In statistical sense polynomial is a linear regression fit. The function that handles linear fitting is called lm. Here is how you can reproduce your results:

lm(y ~ x + I(x^2) + I(x^3))

Unless you are really after the polynomial coefficients it is probably better to use orthogonal polynomials. You can get this fit by doing

lm(y ~ poly(x, 3))

Check out help pages for lm and poly. Hope this helps,

Andy



Andy Jaworski
518-1-01
Process Laboratory
3M Corporate Research Laboratory

E-mail: apjaworski_at_mmm.com
Tel: (651) 733-6092
Fax: (651) 736-3122
                                                                           
             "Jonas Malmros"                                               
             <jonas.malmros_at_gm                                             
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                                       [R] Polynomial fitting              
             01/07/2008 09:16                                              
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I wonder how one in R can fit a 3rd degree polynomial to some data?

Say the data is:

y <- c(15.51, 12.44, 31.5, 21.5, 17.89, 27.09, 15.02, 13.43, 18.18, 11.32) x <- seq(3.75, 6, 0.25)

And resulting degrees of polynomial are:

5.8007 -91.6339 472.1726 -774.2584

THanks in advance!

--
Jonas Malmros
Stockholm University
Stockholm, Sweden


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