(Cubic) Interpolation Spline from "conreg"
From a "conreg" object representing a linear
spline,
interpSplineCon()produces the corresponding (cubic)
spline (via package splines' interpSpline())
by interpolating at the knots, thus “smoothing the kinks”.
isIsplineCon()determines if the spline fulfills the
same convexity / concavity constraints as the underlying
"conreg" object.
interpSplineCon(object, ...) isIsplineCon(object, isp, ...)
object |
an R object as resulting from |
isp |
optionally, the result of |
... |
optional further arguments passed to
|
interpSplineCon()returns the
interpSpline() interpolation spline object.
isIsplineCon()is TRUE (or FALSE),
indicating if the convexity/concavity constraints are fulfilled (in
knot intervals).
Martin Maechler
cc <- conreg(cars[,"speed"], cars[,"dist"], convex=TRUE)
iS <- interpSplineCon(cc)
(isC <- isIsplineCon(cc)) # FALSE: not strictly convex
## Passing the interpolation spline --- if you have it anyway ---
## is more efficient (faster) :
stopifnot(identical(isC,
isIsplineCon(cc, isp = iS)))
## the interpolation spline is not quite convex:
plot(cc)
with(cars, points(dist ~ speed, col = adjustcolor(1, 1/2)))
lines(predict(iS, seq(1,28, by=1/4)),
col = adjustcolor("forest green", 3/4), lwd=2)Please choose more modern alternatives, such as Google Chrome or Mozilla Firefox.