Dear Mr. Rowlingson, Rizopoulos, Jaworski, and Ripley Thank you for your help with the polynomial.
Regards, Jonas On Jan 7, 2008 5:18 PM, Barry Rowlingson <[EMAIL PROTECTED]> wrote: > 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 > -- Jonas Malmros Stockholm University Stockholm, Sweden ______________________________________________ R-help@r-project.org 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.
