[R] Questions about piecewise spline fitting

[Frank E Harrell Jr]

If all you want is a linear spline do something like

   x + pmax(x-a,0) + pmax(x-b,0)

in a model, where knots are a and b.

Frank Harrell


On Tue, 04 Dec 2001 22:05:34 -0800
Gang Liang <gumpleon at hotmail.com> wrote:

> Hi All,
> 
> I want to fit a piecewise spline of degree 1, i.e. a spline consisting of a 
> straight line over each piece. I downloaded the R package pspline, then I 
> have following questions:
> 
> 1. in the program, the degree of the spline is specified by 2*norder-1. Why 
> do they adopt such scheme that we can only fit a spline with odd degree?
> 
> 2. norder cannot be set to 1. Is there any specific reason for doing so?
> 
> Maybe I need to code this by myself. So I'd like to hear your advices.
> 
> Thanks in advance,
> Gang
> 
> 
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-- 
Frank E Harrell Jr              Prof. of Biostatistics & Statistics
Div. of Biostatistics & Epidem. Dept. of Health Evaluation Sciences
U. Virginia School of Medicine  http://hesweb1.med.virginia.edu/biostat
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