[R] Derivative of a splinefun function.

[Rolf Turner]

Is there a way of calculating the derivative of a function returned
by splinefun()?  Such a function is a cubic spline, whence it has a
calculable derivative, but is there a (simple) way of getting at it?

One workaround that I have thought of is to take a fine grid of
points, evaluate the function returned by splinefun() at these
points, put an interpolating spline through these points using
smooth.spline() with spar=0, and then calculate the derivative with
predict(...,deriv=1).

This seems pretty kludgy, and fraught with a certain amount of peril.

Is there a better way?

			cheers,

				Rolf Turner
				rolf at math.unb.ca