[R] Polynomial fitting

[apjaworski at mmm.com]

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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