derivatives of data

[kem]

I have a bunch of data points that resemble a logarithmic
curve, but aren't exactly.

I'm trying to find a way to get the 1st and 2nd derivative
of the data, even though it doesn't have a good y=___ form


Thanks!

 

[Steve Andrews]

Kem,

Have you tried simply using slopes? Put the X values in
Column A and the Y values in Column B. Sort these by
Cloumn A. For approximations to the first derivatives,
assign:
C2=(B2-B1)/(A2-A1)
Then to approximate the second derivatives, assign:
D3=(C3-C2)/(A3-A2)

If any two points share the same X value, you may have to
adjust this to avoid division by zero. While this is not
the most accurate solution, it is an approximation.

 

[Jon Peltier]

I've even extended this to a moving regression, say, the five or seven
points centered on the current row. If the data isn't too badly
behaved, it works pretty well.

- Jon