R help - Jul 2001 - polynomial regression and poly

When doing polynomial regression I believe it is a good idea to use the poly
function to generate orthogonal polynomials.  When doing this in Splus there
is a handy function (transform.poly I think) to convert the coefficients
produced by regression with the poly function back to the original scale.
Has somebody written something similar for R ?  

Robert 


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>  -----Original Message-----
> From: 	Robert.Denham at dnr.qld.gov.au
[mailto:Robert.Denham at dnr.qld.gov.au] 
> Sent:	Monday, 9 July 2001 5:20 PM
> To:	r-help at hypatia.math.ethz.ch
> Subject:	[R] polynomial regression and poly
> 
> When doing polynomial regression I believe it is a good idea to use the
poly
> function to generate orthogonal polynomials.  When doing this in Splus
there
> is a handy function (transform.poly I think) to convert the coefficients
> produced by regression with the poly function back to the original scale.
> Has somebody written something similar for R ?  
> 
> Robert 
Couple of fastidious little points.

If there is such a thing in S-PLUS, I am not aware of it.  What is available
is the ability to evaluate the same polynomials at different x-values.
(See, for examle, poly.raw .)

Also it is not completely clear what you mean by "back to the original
scale".  I presume this means "back to the standard power basis".
The only
facility I am aware of that will do this is the polynom library, but can be
a considerable investment in time to learn how to use it.  There is a fairly
good payoff, though, if you are going to be fiddling with univariate
polynomials like this at all often.

Bill Venables
--
Bill Venables, CMIS
CSIRO Marine Laboratories, PO Box 120, Cleveland, Qld. 4163
Phone: +61 7 3826 7251  Fax: +61 7 3826 7304
Email: Bill.Venables at cmis.csiro.au  http://www.cmis.csiro.au/bill.venables/
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