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Automatically create and update equation that represents the line (polynomial) of data set

  1. #1
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    Automatically create and update equation that represents the line (polynomial) of data set

    Hi everyone, I'm new here so I hope I'm writing in the right Forum...

    I have a data set, with an X and Y axis, that will be changing quite often. I know I can graph the data set and then display equation, but since the data will be changing often I would like it to be done automatically (I don't need the graph just the equation). The equation that best fits the data is a polynomial one (in all cases).

    I found out that "Linest" function can do this, but when I tried using it it gave me a polynomial equation with 4 parts (ax^3+bx^2+cx+d) and the results didn't match the data nor this equation was like the one displayed by the graph (ax^2+bx+c) even though both were based on the same data.

    An excel document has been attached.

    I would appreciate any kind of help on this!

    Thanks!
    Attached Files Attached Files

  2. #2
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    Re: Automatically create and update equation that represents the line (polynomial) of data

    =INDEX(LINEST(NonLinY,NonLinX^{1,2}),1)
    =INDEX(LINEST(NonLinY,NonLinX^{1,2}),1,2)
    =INDEX(LINEST(NonLinY,NonLinX^{1,2}),1,3)

    a,b & c coefficients
    NonLinY = named range of y values
    NonLinX = named range of X values
    Last edited by AndyLitch; 04-10-2013 at 01:42 PM.
    Elegant Simplicity............. Not Always

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