interpSpline             package:splines             R Documentation

Create an Interpolation Spline

Description:

     Create an interpolation spline, either from 'x' and 'y' vectors,
     or from a formula/data.frame combination.

Usage:

     interpSpline(obj1, obj2, bSpline = FALSE, period = NULL,
                  na.action = na.fail)

Arguments:

    obj1: Either a numeric vector of 'x' values or a formula.

    obj2: If 'obj1' is numeric this should be a numeric vector of the
          same length.  If 'obj1' is a formula this can be an optional
          data frame in which to evaluate the names in the formula.

 bSpline: If 'TRUE' the b-spline representation is returned, otherwise
          the piecewise polynomial representation is returned. Defaults
          to 'FALSE'.

  period: An optional positive numeric value giving a period for a
          periodic interpolation spline.

na.action: a optional function which indicates what should happen when
          the data contain 'NA's.  The default action ('na.omit') is to
          omit any incomplete observations.  The alternative action
          'na.fail' causes 'interpSpline' to print an error message and
          terminate if there are any incomplete observations.

Value:

     An object that inherits from class 'spline'. The object can be in
     the B-spline representation, in which case it will be of class
     'nbSpline' for natural B-spline, or in the piecewise polynomial
     representation, in which case it will be of class 'npolySpline'.

Author(s):

     Douglas Bates and Bill Venables

See Also:

     'splineKnots', 'splineOrder', 'periodicSpline'.

Examples:

     require(graphics); require(stats)
     ispl <- interpSpline( women$height, women$weight )
     ispl2 <- interpSpline( weight ~ height,  women )
     # ispl and ispl2 should be the same
     plot( predict( ispl, seq( 55, 75, length.out = 51 ) ), type = "l" )
     points( women$height, women$weight )
     plot( ispl )    # plots over the range of the knots
     points( women$height, women$weight )
     splineKnots( ispl )

