Spline.fit: Polynomial-spline fit with equally-spaced knots
In npmlda: Nonparametric Models for Longitudinal Data

Polynomial-spline fit with equally-spaced knots

1	Spline.fit(Xint, Xvec, Yvec, nKnots = 2, Degree = 3, Wt = 1)

`Xint`	a vector of x interval to generate the local linear fit
`Xvec, Yvec`	numeric vectors of data values, Xvec and Yvec must have the same length.
`nKnots`	number of equally-spaced knots
`Degree`	degree of polynomial splines
`Wt`	a weight vector or a constant. For longitudinal data, Wt=1/N corresponds to measurement uniform weight and Wt=1/(nni) corresponds subject uniform weight.