[R] bs() function of the splines package with intercept=FALSE

[Eddy G.]

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
FALSE, 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 the
_removes_ the first column of the matrix (resulting as expected in a
matrix with df columns).

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

Thanks a lot,

Laurent


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