[R] Questions about piecewise spline fitting

Gang Liang gumpleon at hotmail.com
Thu Dec 6 06:22:58 CET 2001


Thanks a lot for your advices.

My real problem is that the knot positions are not predetermined,  so I have
to deal with this part by myself, :(.

----- Original Message -----
From: "MUGGEO VITO" <vito.muggeo at giustizia.it>
To: "Gang Liang" <gumpleon at hotmail.com>; <r-help at hypatia.math.ethz.ch>
Sent: Wednesday, December 05, 2001 1:39 AM
Subject: Re: [R] Questions about piecewise spline fitting


> Hi,
> What you need is just the bs() or ns() functions in the library splines in
> the R-software. You have to specify the knots and can specify the degree.
> For instance:
>
> library(splines)
> bs(1:20, knots=c(5,11), degree=1) #performs three #straight lines with
> break-point at x=5 and 11 for the variable 1:20
> lm(y~bs(1:20, knots=c(5,11), degree=1)) #piecewise linear regression
>
> Common "problem" is that the beta parameters for the pseudo-variables
> inducted by bs() are not interpretable (i.e. in linear case they don't
> represents the slopes in each piece).
> best,
> vito
>
>
> ----- Original Message -----
> From: "Gang Liang" <gumpleon at hotmail.com>
> To: <r-help at hypatia.math.ethz.ch>
> Sent: Wednesday, December 05, 2001 7:05 AM
> Subject: [R] Questions about piecewise spline fitting
>
>
> > 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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