predict.bSpline {splines}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, ...)

Arguments

object An object that inherits from the bSpline or the polySpline class. For plot.spline this argument is called x.
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. For plot.spline the x argument is as described under object above.
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.
... predict: further arguments passed to or from other methods.
plot: additional graphical parameters (see link{par}).

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

See Also

xyVector, interpSpline, periodicSpline

Examples

data( women )
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)
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