

   MMoonnoottoonnee IInnvveerrssee SSpplliinnee

        backSpline(object)

   AArrgguummeennttss::

     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 B-spline representation or the
             piecewise polynomial representation.  The spline
             is checked to see if represents a monotone func-
             tion.

   DDeessccrriippttiioonn::

        Create a monotone inverse of a monotone natural spline.

   VVaalluuee::

        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.

   AAuutthhoorr((ss))::

        Douglas Bates and Bill Venables

   SSeeee AAllssoo::

        `interpSpline'

   EExxaammpplleess::

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

