Pete:
Excel uses Bezier curves to smooth data. If you are willing to settle for
cubic splines as a smooth, then refer to my code; sorry I lost the url, but
a google search in the excel newsgroups under Braden and cubic spline should
do the trick. The code returns several derivatives of any set of points in a
cubic spline of your data.
Of course, if you know the function, then post it if you cannot
differentiate it.
Regards,
Dave Braden
