periodicSpline
Create a Periodic Interpolation Spline

### Description

Creates a periodic interpolation spline.

### Usage

    periodicSpline(obj1, obj2, knots, period = 2 * pi, ord = 4)
    ## Default S3 method:
    periodicSpline(obj1, obj2, knots, period = 2 * pi, ord = 4)
    ## S3 method for class 'formula':
    periodicSpline(obj1, obj2, knots, period = 2 * pi, ord = 4)

### Arguments

obj1 | a numeric vector or a formula with the form of "y~x".
obj2 | a numeric vector with the same length as obj1, or an optional data frame to evaluate the terms when obj1 is a formula. When obj1 is a formula and obj2 is missing, the sys.parent(1) is used as evaluation parent frame.
knots | a numeric vector. Used to design interpolation spline.
period | an optional value specifying the period for a periodic interpolation spline.
ord | a positive integer. Must be bigger than 2, and at most the number of knots of obj1.

### Details

The elements of obj1 must be distinct in the function periodicSpline.default.

- If knots is missing, knots is composed by c(x[(lenx - (ord - 2)):lenx] - period, x, x[1L:ord] + period)
- If knots is not missing, period is rewritten by knots[length(knots) - ord + 1] - knots[1L].

The range between the first value and the last value of obj1 should be in one period.
Value
returns a list object of class c("pbSpline", "bSpline", "spline") that contains four components:

- "knots"
- "coefficients"
- "order"
- "period" with the attribute "formula"

See Also
interpSpline, splineDesign.
Examples

    qtr <- c(1, 2, 3, 4)
    sales <- c(101, 102, 113, 104)
    # fit a smooth seasonal pattern to sales
    pS <- periodicSpline(qtr, sales, period = 4)
    # interpolate/extrapolate to new times
    predict(pS, seq(3,7,by=1/4))

Package splines version 6.1.5-18
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