# Microsoft Office Application Help - Excel Help forum > Excel Formulas & Functions >  > [SOLVED] How do I calculate the inflection point?

## 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 rgoyan@sfu.ca

----------


## 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.
--
Gary''s Student


"rgoyan" wrote:

> 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 rgoyan@sfu.ca

----------


## 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.

"Gary''s Student" wrote:

> 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.
> --
> Gary''s Student
>
>
> "rgoyan" wrote:
>
> > 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 rgoyan@sfu.ca

----------


## 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.
--
Gary's Student


"rgoyan" wrote:

> 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.
>
> "Gary''s Student" wrote:
>
> > 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.
> > --
> > Gary''s Student
> >
> >
> > "rgoyan" wrote:
> >
> > > 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 rgoyan@sfu.ca

----------

