[R] bs() function of the splines package

[Eddy G.]

Laurent 	  14 juin 12:02     afficher les options
De : "Laurent" <eddy_l... at hotmail.com> - Rechercher les messages de cet 
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Date : Tue, 14 Jun 2005 03:02:37 -0700
Local : Mar 14 juin 2005 12:02
Objet : bs() function of the splines package
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Hello,

I'm implementing a function using non uniform B-Splines. Looking at the
code of the bs() function, I realized that if the intercept was set to
TRUE, the behavior of the function was the following (df is the number
of degrees of freedom that I believe can be interpreted as the number
of control points):

- Compute df- ord + 1 _internal_ knots (ord is the order of the spline)
- Add ord times the boundaries values at each extrem of the knots
vector.
- Compute the design matrix on this vector.

This results in a design matrix with df+1 columns. The bs function then
_removes_ the first column of the matrix (resulting as expected in a
matrix with df columns).

I'm a bit confused, does anyone see a mathematical justification to
this manipulation?

In this case, is it licit tu use df- ord + 2 internal knots and remove
the last columns too?

Thanks a lot,

Laurent