fields (version 1.2)

splint: Cubic spline interpolation

Description

A fast, FORTRAN based function for cubic spline interpolation.

Usage

splint(x, y, xgrid, derivative=0)

Arguments

x

The x values that define the curve or a two column matrix of x and y values.

y

The y values that are paired with the x's.

xgrid

The grid to evaluate the fitted cubic interpolating curve.

derivative

Indicates whether the function or a a first or second derivative should be evaluated.

Value

• A vector consisting of the spline evaluated at the grid values.

References

See Additive Models by Hastie and Tibshriani.

Details

Fits a piecewise interpolating cubic polynomial to the x and y values assuming that the second and third derivatives are zero at the range of the x values. For this reason extrapolation outside the range of the x values will be a linear function.

See Also

sreg, Tps

Examples

x<- seq( 0, 120,,200)

splint(rat.diet$t, rat.diet$trt,x )-> y

plot( rat.diet$t, rat.diet$trt)
lines( x,y)
#( this is weird!)