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interpSpline: Create an Interpolation Spline

interpSpline

R Documentation

Create an Interpolation Spline

Description

Create an interpolation spline, either from x and y vectors (default method), or from a formula / data.frame combination (formula method).

Usage

interpSpline(obj1, obj2, bSpline = FALSE, period = NULL,
             ord = 4L,
             na.action = na.fail, sparse = FALSE)

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.
`ord`	an integer specifying the spline order, the number of coefficients per interval. ord = d+1 where d is the degree polynomial degree. Currently, only cubic splines (`ord = 4`) are implemented.
`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.
`sparse`	logical passed to the underlying `splineDesign`. If true, saves memory and is faster when there are more than a few hundred points.

Value

An object that inherits from (S3) 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

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 )