
R Under development (unstable) (2020-12-17 r79644) -- "Unsuffered Consequences"
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> library(survival)
> library(splines)
> 
> # the nsk function should give the same solution as ns, but with a different
> #  parameterization
> #
> xx <- runif(500, 1, 100)
> yy <- 10*log(xx) + rnorm(500, 0, 2)
> tdata <- data.frame(xx=xx, yy=yy)
> fit1 <- lm(yy ~ ns(xx, df=4), tdata, model=TRUE)
> fit2 <- lm(yy ~ nsk(xx, df=4, b=0), tdata)
> all.equal(predict(fit1), predict(fit2))  # same solution
[1] TRUE
> 
> xattr <- attributes(fit1$model[[2]])
> allknots <- sort(c(xattr$knots, xattr$Boundary.knots)) # knots that were used
> pred.knot <- predict(fit1, newdata=list(xx=allknots))
> all.equal(pred.knot[-1] - pred.knot[1], coef(fit2)[-1],
+           check.attributes = FALSE)
[1] TRUE
> 
> 
> proc.time()
   user  system elapsed 
  0.857   0.036   0.887 
