# cSplineDes {mgcv}

### Description

Uses `splineDesign`

to set up the model matrix for a cyclic B-spline basis.

### Usage

cSplineDes(x, knots, ord = 4)

### Arguments

- 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.

### Details

The routine is a wrapper that sets up a B-spline basis, where the basis functions wrap at the first and last knot locations.

### See Also

`cyclic.p.spline`

### Examples

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!")

Documentation reproduced from package mgcv, version 1.8-11. License: GPL (>= 2)