mixAK (version 2.2)

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")

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.

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.

See Also

bs.

Examples

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)