splint {funfits}R Documentation

Cubic spline interpolation

Description

Fits a piecewise 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.

Usage

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

Arguments

x The x values the 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.

See Also

spreg, sreg, tps

Examples

splint(ozone$x[,1],ozone$y,seq(min(ozone$x[,1]),max(ozone$x[,1]),,40)) -> fit 
# evaluate cubic spline to ozone at longitude values on grid of 
# longitude values


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