R: Create a Periodic Interpolation Spline

periodicSpline {splines}

R Documentation

Create a Periodic Interpolation Spline

Description

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

Usage

periodicSpline(obj1, obj2, knots, period, ord)

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.

knots

An optional numeric vector of knot positions.

period

A positive numeric value giving the period for the periodic spline. Defaults to 2 * pi.

ord

A positive integer giving the order of the spline. Defaults to 4. See ?splineOrder for a definition of the order of a spline.

Value

An object that inherits from class spline. The object can be in the B-spline representation, in which case it will be a pbSpline object, or in the piecewise polynomial representation (a ppolySpline object).

Author(s)

Douglas Bates and Bill Venables

Examples

library( splines )
xx <- seq( -pi, pi, len = 16 )[-1]
yy <- sin( xx )
frm <- data.frame( xx, yy )
print( pispl <- periodicSpline( xx, yy, period = 2 * pi ) )
print( pispl2 <- periodicSpline( yy ~ xx, frm, period = 2 * pi ) )
# pispl and pispl2 should be the same
plot( predict( pispl, seq(-3*pi, 3*pi, len = 101) ), type = "l" )
plot( pispl )          # displays over one period

[Package splines version 1.1 ]