How do I calculate the inflection point?

Discussion in 'Microsoft Excel Worksheet Functions' started by Guest, Aug 22, 2006.

  1. Guest

    Guest Guest

    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
     
    Guest, Aug 22, 2006
    #1
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  2. Guest

    Guest Guest

    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
     
    Guest, Aug 23, 2006
    #2
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  3. Guest

    Guest Guest

    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
     
    Guest, Aug 23, 2006
    #3
  4. Guest

    Guest Guest

    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
     
    Guest, Aug 23, 2006
    #4
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