Evaluate cyclic B spline basis
Uses splineDesign to set up the model matrix for a cyclic B-spline basis.
cSplineDes(x, knots, ord = 4, derivs=0)
x |
covariate values for smooth. |
knots |
The knot locations: the range of these must include all the data. |
ord |
order of the basis. 4 is a cubic spline basis. Must be >1. |
derivs |
order of derivative of the spline to evaluate, between 0 and |
The routine is a wrapper that sets up a B-spline basis, where the basis functions wrap at the first and last knot locations.
A matrix with length(x) rows and length(knots)-1 columns.
Simon N. Wood simon.wood@r-project.org
require(mgcv)
## create some x's and knots...
n <- 200
x <- 0:(n-1)/(n-1);k<- 0:5/5
X <- cSplineDes(x,k) ## cyclic spline design matrix
## plot evaluated basis functions...
plot(x,X[,1],type="l"); for (i in 2:5) lines(x,X[,i],col=i)
## check that the ends match up....
ee <- X[1,]-X[n,];ee
tol <- .Machine$double.eps^.75
if (all.equal(ee,ee*0,tolerance=tol)!=TRUE)
stop("cyclic spline ends don't match!")
## similar with uneven data spacing...
x <- sort(runif(n)) + 1 ## sorting just makes end checking easy
k <- seq(min(x),max(x),length=8) ## create knots
X <- cSplineDes(x,k) ## get cyclic spline model matrix
plot(x,X[,1],type="l"); for (i in 2:ncol(X)) lines(x,X[,i],col=i)
ee <- X[1,]-X[n,];ee ## do ends match??
tol <- .Machine$double.eps^.75
if (all.equal(ee,ee*0,tolerance=tol)!=TRUE)
stop("cyclic spline ends don't match!")Please choose more modern alternatives, such as Google Chrome or Mozilla Firefox.