[R] Cubic splines in package "mgcv"

Simon Wood s.wood at bath.ac.uk
Sun Jan 6 17:59:35 CET 2008

On Wednesday 26 December 2007 04:14, Kunio takezawa wrote:
> R-users
> E-mail: r-help at r-project.org
>    My understanding is that package "mgcv" is based on
> "Generalized Additive Models: An Introduction with R (by Simon N. Wood)".
> On the page 126 of this book, eq(3.4) looks a quartic equation with respect
> to
> "x", not a cubic equation. I am wondering if all routines which uses
> cubic splines in mgcv are based on this quartic equation.
--- No, `mgcv' does not use the basis given on page 126. See sections 
4.1.2-4.1.8 of the same book for the bases used.

>    In my humble opinion, the '^4' in the first term
> of the second line of this equation should be '^3'.
--- Perhaps take a look at section 2.3.3 of Gu (2002) "Smoothing Spline ANOVA" 
for a bit more detail on this/

> K. Takezawa

> Simon Wood, Mathematical Sciences, University of Bath, Bath, BA2 7AY UK
> +44 1225 386603  www.maths.bath.ac.uk/~sw283

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