backSpline {splines}  R Documentation 
Create a monotone inverse of a monotone natural spline.
backSpline(object)
object 
an object that inherits from class nbSpline or
npolySpline . That is, the object must represent a natural
interpolation spline but it can be either in the Bspline
representation or the piecewise polynomial one. The spline is
checked to see if it represents a monotone function.

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
ispl < interpSpline( women$height, women$weight ) bspl < backSpline( ispl ) plot( bspl ) # plots over the range of the knots points( women$weight, women$height )