DPpackage (version 1.1-7.4)

ps: Specify a smoothing spline fit in a PSgam formula

Description

A symbolic wrapper to indicate a smooth term in a formula argument to PSgam

Usage

ps(..., k=50,degree=3,pord=1)

Arguments

...

the predictors.

k

an integer giving the number of knots. The number of basis functions is k+degree.

degree

an integer giving the degree of the B-splines, e.g. degree=3 gives a cubic spline.

pord

an integer giving the order of difference penalty.

Value

ps returns the vectors of predictors, endowed with a number of attributes. The vector itself is used in the construction of the model matrix.

Note that ps does not do the smoothing; it simply sets things up for PSgam.

References

Eilers, P.H.C. and Marx, B.D. (1996) Flexible Smoothing with B-splines and penalties. Statistical Science, 11(2): 89-121.

Examples

# NOT RUN {
   # fit Start using a smoothing spline with 4 df.
     y ~ Age + ps(Start, degree=4)
   # fit log(Start) using a smoothing spline with 5 df.
     y ~ Age + ps(log(Start), degree=5)
# }