[R] Puzzling coefficients for linear fitting to polynom

From: Firas Swidan, PhD <frsswdn_at_gmail.com>
Date: Fri, 07 Mar 2008 10:16:06 +0200


Hi,

I can not comprehend the linear fitting results of polynoms. For example, given the following data (representing y = x^2):

> x <- 1:3
> y <- c(1, 4, 9)

performing a linear fit

> f <- lm(y ~ poly(x, 2))

gives weird coefficients:

> coefficients(f)

(Intercept) poly(x, 2)1 poly(x, 2)2
  4.6666667 5.6568542 0.8164966

However the fitted() result makes sense:

> fitted(f)

1 2 3
1 4 9

This is very confusing. How should one understand the result of coefficients()?

Thanks for any tips,
Firas.

-- 
Firas Swidan, PhD
Founder and CEO
Olymons: Blessing Machines with Vision (TM)
http://www.olymons.com
P.O.Box 8125
Nazareth 16480
Israel
Cell: +.972.(0)54.733.1788

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Received on Fri 07 Mar 2008 - 08:20:59 GMT

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