periodicSpline
Create a Periodic Interpolation Spline
Create a periodic interpolation spline, either from x
and
y
vectors, or from a formula/data.frame combination.
- Keywords
- models
Usage
periodicSpline(obj1, obj2, knots, period = 2*pi, ord = 4)
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. Ifobj1
is a formula this can be an optional data frame in which to evaluate the names in the formula. - knots
- optional numeric vector of knot positions.
- period
- positive numeric value giving the period for the
periodic spline. Defaults to
2 * pi
. - ord
- integer giving the order of the spline, at least 2. 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).
See Also
Examples
library(splines)
require(graphics); require(stats)
xx <- seq( -pi, pi, length.out = 16 )[-1]
yy <- sin( xx )
frm <- data.frame( xx, yy )
pispl <- periodicSpline( xx, yy, period = 2 * pi)
pispl
pispl2 <- periodicSpline( yy ~ xx, frm, period = 2 * pi )
stopifnot(all.equal(pispl, pispl2)) # pispl and pispl2 are the same
plot( pispl ) # displays over one period
points( yy ~ xx, col = "brown")
plot( predict( pispl, seq(-3*pi, 3*pi, length.out = 101) ), type = "l" )
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