Bsplines.R
From Organic Design wiki
Code snipits and programs written in R, S or S-PLUS
- p38
pos <- function(x) ifelse(x>0, x, 0) x <- 1:7 y <- c(8,3,8,5,9,14,11) knot <- 4 plot(x,y) X <- cbind("int"=1,"x"=x,"x2"=x^2,"x3"=x^3, "xknot"=pos(x-knot)^3) fit <- lm(y~X-1) xx <- seq(1,7, length=200) XX <- cbind("Xint"=1,"Xx"=xx, "Xx2"=xx^2, "Xx3"=xx^3, "Xxknot"=pos(xx-knot)^3) lines(xx, predict(fit, as.data.frame(XX))) # Bug here abline(v=knot, lty=2) X
- p41
par(mfrow=c(2,1)) knots <- c(1:3,5,7,8,10) atx <- seq(0:11, by=0.1) for(ord in 1:4) { B <- bs(x=atx, degree=ord, knots=knots, intercept=TRUE, Boundary.knots=c(0,11)) matplot(atx, B[,1], type="l", ylim=0:1, lty=2) matlines(atx, B[,-1], col=1, lty=1) title(paste("B splines of order", ord)) abline(v=knots, lty=2) }