Dimitris Rizopoulos wrote:
> try this:
>
> 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)
> coef(lm(y ~ x + I(x^2) + I(x^3)))
Or use the 'poly' function:
> coef(lm(x~poly(y,3)))
(Intercept) poly(y, 3)1 poly(y, 3)2 poly(y, 3)3
4.8750000 -0.6233293 0.0312415 -0.6464533
But hmmm those aren't the same coefficients?
Because you need to use 'raw=TRUE' if you really want to fit the raw
powers rather than orthogonal polynomials (which are better behaved than
fitting the raw powers):
> coef(lm(y~poly(x,3,raw=TRUE)))
(Intercept) poly(x, 3, raw = TRUE)1 poly(x, 3, raw = TRUE)2
-774.258364 472.172611 -91.633939
poly(x, 3, raw = TRUE)3
5.800653
And there's your coefficients. See help(poly) for more.
Barry
______________________________________________
[email protected] mailing list
https://stat.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.
