cubic spline/smoother with nlme

-----Original Message-----
From: r-help-bounces at stat.math.ethz.ch 
[mailto:r-help-bounces at stat.math.ethz.ch] On Behalf Of Peter Dalgaard
Sent: Wednesday, November 10, 2004 4:54 PM
To: Suzette Blanchard
Cc: r-help at stat.math.ethz.ch
Subject: Re: [R] cubic spline/smoother with nlme


Suzette Blanchard <suzette at sdac.harvard.edu> writes:

Greetings,  I would like to use a cubic spline
or smoother to model the fixed effects within
nlme.  So far the only smoother I have been able
to get to run successfully in nlme is smooth().

I tried smooth.spline:
   fixed=list(lKa~1,lCL~smooth.spline(BSA, df=3))
   the error I got was the following.
   Error in model.frame(formula, rownames, variables, 

varnames, extras,

   extranames,  :  invalid variable type

Can anyone suggest a cubic spline that would work within
this context?

The fixed-knots ones (ns(), bs()) should work (and did so in at least
one case a couple of years ago...). These are linear, so lme() is used
rather than nlme(), unless of course you have other parts that need to
be modeled nonlinearly.

-- 
   O__  ---- Peter Dalgaard             Blegdamsvej 3  
  c/ /'_ --- Dept. of Biostatistics     2200 Cph. N   
 (*) \(*) -- University of Copenhagen   Denmark      Ph: 
(+45) 35327918
~~~~~~~~~~ - (p.dalgaard at biostat.ku.dk)             FAX: 
(+45) 35327907