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predict.bSpline: Evaluate a Spline at New Values of x

predict.bSpline

R Documentation

Evaluate a Spline at New Values of x

Description

The predict methods for the classes that inherit from the virtual classes bSpline and polySpline are used to evaluate the spline or its derivatives. The plot method for a spline object first evaluates predict with the x argument missing, then plots the resulting xyVector with type = "l".

Usage

## S3 method for class 'bSpline'
predict(object, x, nseg = 50, deriv = 0, ...)
## S3 method for class 'nbSpline'
predict(object, x, nseg = 50, deriv = 0, ...)
## S3 method for class 'pbSpline'
predict(object, x, nseg = 50, deriv = 0, ...)
## S3 method for class 'npolySpline'
predict(object, x, nseg = 50, deriv = 0, ...)
## S3 method for class 'ppolySpline'
predict(object, x, nseg = 50, deriv = 0, ...)

Arguments

`object`	An object that inherits from the `bSpline` or the `polySpline` class.
`x`	A numeric vector of `x` values at which to evaluate the spline. If this argument is missing a suitable set of `x` values is generated as a sequence of `nseq` segments spanning the range of the knots.
`nseg`	A positive integer giving the number of segments in a set of equally-spaced `x` values spanning the range of the knots in `object`. This value is only used if `x` is missing.
`deriv`	An integer between 0 and `splineOrder(object) - 1` specifying the derivative to evaluate.
`...`	further arguments passed to or from other methods.

Value

an xyVector with components

`x`	the supplied or inferred numeric vector of `x` values
`y`	the value of the spline (or its `deriv`'th derivative) at the `x` vector

Author(s)

Douglas Bates and Bill Venables

Examples

require(graphics); require(stats)
ispl <- interpSpline( weight ~ height,  women )
opar <- par(mfrow = c(2, 2), las = 1)
plot(predict(ispl, nseg = 201),     # plots over the range of the knots
     main = "Original data with interpolating spline", type = "l",
     xlab = "height", ylab = "weight")
points(women$height, women$weight, col = 4)
plot(predict(ispl, nseg = 201, deriv = 1),
     main = "First derivative of interpolating spline", type = "l",
     xlab = "height", ylab = "weight")
plot(predict(ispl, nseg = 201, deriv = 2),
     main = "Second derivative of interpolating spline", type = "l",
     xlab = "height", ylab = "weight")
plot(predict(ispl, nseg = 401, deriv = 3),
     main = "Third derivative of interpolating spline", type = "l",
     xlab = "height", ylab = "weight")
par(opar)