[R] lm coefficients

[Prof Brian Ripley]

Do read ?poly: you have orthogonal polynomials.

On Tue, 3 Feb 2004, Timur Elzhov wrote:

> Dear R experts,
> 
> Excuse me if my question will be stupid...
> I'd like to fit data with x^2 polynomial:
> 
> d <- read.table(file = "Oleg.dat", head = TRUE)
> d
>   X         T
>   3720.00   4.113
>   3715.00   4.123
>   3710.00   4.132
>   ...
> 
> out <- lm(T ~ poly(X, 4), data = d)

You asked for 4 and got 2?  Really?

> out
>   Call:
>   lm(formula = T ~ poly(X, 2), data = d)
>   
>   Coefficients:
>   (Intercept)  poly(X, 2)1  poly(X, 2)2  
>         9.803     -108.075       51.007  
> 
> So, d$T best fitted with function
>   9.803 -108.075 * X + 51.007 * X^2,
> yes?

No!

-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272866 (PA)
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