backSpline {splines} | R Documentation |
Create a monotone inverse of a monotone natural spline.
backSpline(object)
object |
an object that inherits from class |
An object of class polySpline
that contains the piecewise
polynomial representation of a function that has the appropriate
values and derivatives at the knot positions to be an inverse of the
spline represented by object
. Technically this object is not a
spline because the second derivative is not constrained to be
continuous at the knot positions. However, it is often a much better
approximation to the inverse than fitting an interpolation spline to
the y/x pairs.
Douglas Bates and Bill Venables
require(graphics)
ispl <- interpSpline( women$height, women$weight )
bspl <- backSpline( ispl )
plot( bspl ) # plots over the range of the knots
points( women$weight, women$height )