stats (version 3.6.2)

# predict.smooth.spline: Predict from Smoothing Spline Fit

## Description

Predict a smoothing spline fit at new points, return the derivative if desired. The predicted fit is linear beyond the original data.

## Usage

```# S3 method for smooth.spline
predict(object, x, deriv = 0, …)```

## Arguments

object

a fit from `smooth.spline`.

x

the new values of x.

deriv

integer; the order of the derivative required.

further arguments passed to or from other methods.

## Value

A list with components

x

The input `x`.

y

The fitted values or derivatives at `x`.

`smooth.spline`

## Examples

Run this code
``````# NOT RUN {
require(graphics)

attach(cars)
cars.spl <- smooth.spline(speed, dist, df = 6.4)
# }
# NOT RUN {
## "Proof" that the derivatives are okay, by comparing with approximation
diff.quot <- function(x, y) {
## Difference quotient (central differences where available)
n <- length(x); i1 <- 1:2; i2 <- (n-1):n
c(diff(y[i1]) / diff(x[i1]), (y[-i1] - y[-i2]) / (x[-i1] - x[-i2]),
diff(y[i2]) / diff(x[i2]))
}

xx <- unique(sort(c(seq(0, 30, by = .2), kn <- unique(speed))))
i.kn <- match(kn, xx)   # indices of knots within xx
op <- par(mfrow = c(2,2))
plot(speed, dist, xlim = range(xx), main = "Smooth.spline & derivatives")
lines(pp <- predict(cars.spl, xx), col = "red")
points(kn, pp\$y[i.kn], pch = 3, col = "dark red")
mtext("s(x)", col = "red")
for(d in 1:3){
n <- length(pp\$x)
plot(pp\$x, diff.quot(pp\$x,pp\$y), type = "l", xlab = "x", ylab = "",
col = "blue", col.main = "red",
main = paste0("s" ,paste(rep("'", d), collapse = ""), "(x)"))
mtext("Difference quotient approx.(last)", col = "blue")
lines(pp <- predict(cars.spl, xx, deriv = d), col = "red")
# }
# NOT RUN {
points(kn, pp\$y[i.kn], pch = 3, col = "dark red")
abline(h = 0, lty = 3, col = "gray")
}
detach(); par(op)
# }
``````

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