

   CCuubbiicc sspplliinnee iinntteerrppoollaattiioonn

        splint(x, y, xgrid, derivative=0)

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

          x: The x values the define the curve or a two column
             matrix of x and y values.

          y: The y values that are paired with the x's.

      xgrid: The grid to evaluate the fitted cubic interpolat-
             ing curve.

   derivative: Indicates whether the function or a a first or
             second derivative should be evaluated.

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

        Fits a piecewise cubic polynomial to the x and y values
        assuming that the second and third derivatives are zero
        at the range of the x values. For this reason extrapo-
        lation outside the range of the x values will be a lin-
        ear function.

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

        A vector consisting of the spline evaluated at the grid
        values.

   RReeffeerreenncceess::

        See Additive Models by Hastie and Tibshriani.

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

        spreg, sreg, tps

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

        splint(ozone$x[,1],ozone$y,seq(min(ozone$x[,1]),max(ozone$x[,1]),,40)) -> fit
        # evaluate cubic spline to ozone at longitude values on grid of
        # longitude values

