Derivatives

[Eutrapelia]

Does anyone have a relatively precise method for calculating derivatives in
Excel. There is of course the option of using the (A3-A1)/(B3-B1) to find
and approximation at B2, but does anyone have anything that is a bit more
reliable?

Thanks

 

[Bernard Liengme]

You could use LINEST (see my website) to find a polynomial of best fit and
then evaluate the differential of the equation at the point of interest
best wishes

 

[Eutrapelia]

Thanks for your help. Is there any way to get the LINEST function to work
iteratively with a macro. I am writing an optimization spreadsheet that
finds the minimum of a function over a range using successive parabolic fits
to three data points along the range. A curve is fitted to the three data
points (x(k-2), x(k-1), and x(k)) and the minimum of the curve is then found.
That minimum then becomes the new x(k) and the process is repeated until a
certain level of convergence is found. I want to be able to do this with a
single macro command.

I would be grateful for any suggestions.