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ksk_1059423212-Amethyst
12-Amethyst
February 20, 2023
Solved

Fit function to plotted graph (that resembles the shape of a haft circle)

Hi

I have plotted the results from two vectors. The graph resembles the shape of a half circle and I would like to find a function that fits the data so intersection points can be determined for other functions. 

I have tried many different curve-fitting tools but can't find a proper one that works. 

 

I'm  thankful for any help!

 

 

 

 

Werner_E
Werner_EAnswer
25-Diamond I
February 20, 2023

I get slightly different values using CurveExpert Pro

Werner_E_0-1676906036862.png

And I get similar values in Prime using genfit() (though genfit is VERY sensible wrt the guess values).

Werner_E_1-1676906149759.png

BTW, as we can see far to the right of the Prime sheet how the data is actually calculated it should not surprise that a sinusoidal fit is suggested by CurveExpert 😉

 

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17 replies

Fred_Kohlhepp23-Emerald I
23-Emerald I
February 20, 2023

If I digitize the data, then rotate it so X is a function of Y, and send it to CurveExpert,, I get

Fred_Kohlhepp_0-1676896848850.png

Which has the form

Fred_Kohlhepp_1-1676896917526.png

Prime 4 attached

 

 

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    Werner_E
    Werner_E25-Diamond IAnswer
    25-Diamond I
    February 20, 2023

    I get slightly different values using CurveExpert Pro

    Werner_E_0-1676906036862.png

    And I get similar values in Prime using genfit() (though genfit is VERY sensible wrt the guess values).

    Werner_E_1-1676906149759.png

    BTW, as we can see far to the right of the Prime sheet how the data is actually calculated it should not surprise that a sinusoidal fit is suggested by CurveExpert 😉

     

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    ksk_1059423212-AmethystAuthor
    12-Amethyst
    February 21, 2023

    Wow! Thanks for the good explanation! 

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    Fred_Kohlhepp23-Emerald I
    23-Emerald I
    February 24, 2023

    It is possible to define functions rather than vectors for your plots:

    Fred_Kohlhepp_0-1677257723199.png

    I've done it in the attached Prime 8 Express sheet.

    Attempts to solve for the intersection (in Express) have failed; maybe someone with a solve block capability?

    Note that it's possible to create functions only using the parameter "y", which would result in a single intersection point.  I introduced a second variable (l_k) hoping to be able to trace the intersection point as a function of that variable.

    Fred_Kohlhepp_1-1677258248309.png 

    If only one point is required . . .

     

    Good Luck!

     

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      Werner_E
      Werner_E25-Diamond I
      25-Diamond I
      February 24, 2023

      Here you are ...

      As solve block does the job pretty well but is a bit  sensitive wrt the guess values

      Werner_E_1-1677270927150.png

       

       

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