| % File src/library/splines/man/backSpline.Rd |
| % Part of the R package, https://www.R-project.org |
| % Copyright 1995-2007 R Core Team |
| % Distributed under GPL 2 or later |
| |
| \name{backSpline} |
| \alias{backSpline} |
| \title{Monotone Inverse Spline} |
| \description{ |
| Create a monotone inverse of a monotone natural spline. |
| } |
| \usage{ |
| backSpline(object) |
| } |
| \arguments{ |
| \item{object}{an object that inherits from class \code{nbSpline} or |
| \code{npolySpline}. That is, the object must represent a natural |
| interpolation spline but it can be either in the B-spline |
| representation or the piecewise polynomial one. The spline is |
| checked to see if it represents a monotone function. |
| } |
| } |
| \value{ |
| An object of class \code{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 \code{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. |
| } |
| \author{Douglas Bates and Bill Venables} |
| \seealso{ |
| \code{\link{interpSpline}} |
| } |
| \examples{ |
| 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 ) |
| } |
| \keyword{ models } |