BsBasis: B-spline basis

Description

It creates a B-spline basis based on a specific dataset. B-splines are assumed to have common boundary knots and equidistant inner knots.

Usage

BsBasis(degree, ninner, knotsBound, knots, intercept=FALSE,
        x, tgrid, Bname="B", plot=FALSE, lwd=1,
        col="blue", xlab="Time", ylab="B(t)",
        pch=16, cex.pch=1, knotcol="red")

Value

A matrix with the B-spline basis. Number of rows is equal to the length of x.

Additionally, the resulting matrix has attributes:

degree: B-spline degree
intercept: logical indicating the presence of the intercept B-spline
knots: a numeric vector of knots
knotsInner: a numeric vector of innner knots
knotsBound: a numeric vector of boundary knots
df: the length of the B-spline basis (number of columns of the resulting object).
tgrid: a numeric vector which can be used on x-axis to plot the basis.
Xgrid: a matrix with length(tgrid) rows and df columns which can be used to plot the basis.

Arguments

degree: degree of the B-spline.
ninner: number of inner knots.
knotsBound: 2-component vector with boundary knots.
knots: knots of the B-spline (including boundary ones). If knots is given ninner and knotsBound are ignored.
intercept: logical, if FALSE, the first basis B-spline is removed from the B-spline basis and it is assumed that intercept is added to the statistical models used afterwards.
x: a numeric vector to be used to create the B-spline basis.
tgrid: if given then it is used to plot the basis.
Bname: label for the created columns with the B-spline basis.
plot: logical, if TRUE the B-spline basis is plotted.
lwd, col, xlab, ylab: arguments passed to the plotting function.
pch, cex.pch: plotting character and cex used to plot knots
knotcol: color for knots on the plot with the B-spline basis.

Author

Arnošt Komárek arnost.komarek@mff.cuni.cz

Examples

Run this code

set.seed(20101126)
t <- runif(20, 0, 100)

oldPar <- par(mfrow=c(1, 2), bty="n")
Bs <- BsBasis(degree=3, ninner=3, knotsBound=c(0, 100), intercept=FALSE,
              x=t, tgrid=0:100, plot=TRUE)
print(Bs)

Bs2 <- BsBasis(degree=3, ninner=3, knotsBound=c(0, 100), intercept=TRUE,
               x=t, tgrid=0:100, plot=TRUE)
print(Bs2)
par(oldPar)

print(Bs)
print(Bs2)