How do I calculate the inflection point?

R

rgoyan

I am trying to calculate the first derivative of a curve in excel to
determine the inflection point. I know how to do this in Sigmaplot, but my
students only have access to excel.

Please reply to [email protected]
 
G

Gary''s Student

The curve in Excel is just a sequence of data points. Fit a curve to the
data (mathematically expression). Take the 2nd derivatiove of the curve and
look for points where the 2nd derivative goes thru zero while switching signs.
 
R

rgoyan

I found a way to do it long hand (so to speak). I was hoping that excel had
a function that would just take the data plot a derivative curve for me from
which I could pick out the maximum. Do you know of any way to do this that
doesn't involve curve fitting? This is for a pH titration curve.

Thanks for your help.
 
G

Gary''s Student

Estimating the first derivative is not diffiuclt. Let's say the x's are in
column A and the y's are in column B. In C2 enter:

=(B3-B1)/(A3-A1) and copy down the column. This is an estimate of dy/dx
at the point [A2,B2]. In a similar fashion you can estimate the second
derivative in column D.
 
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