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I Question about fitting periodic data

  1. Apr 22, 2016 #1
    My experience with data fitting is poor so I am in real need for help.
    The potential in the following is periodic over [0,Pi]
    -TvEuURwmnboNeDc1hN8aBhBkWcK4kYbjZhf4lPAZeE6fUeQvsEFcp56MUrHXa2Y9tATurVnxQLgm3EVsdR=w360-h211-no.gif
    I need to find a fitting function that I can use to perform further mathematics. Fourier series does not work, but a 40-degree polynomial give the following fit
    9iL8mytaLHj6GJp882dVJnCy-Nqr62qTLGS0dNx4JEdCKuJWhwD_DRFy3JoUr6X6kWcId3eSMQshzo9jtIM=w360-h215-no.gif
    However, the polynomial does not preserve its periodicity over the cycle. Could someone please advice what I should do to get a good fitting function for my data?
     
  2. jcsd
  3. Apr 22, 2016 #2

    micromass

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    Fitting with a polynomial with degree larger than 3 is a really bad idea.

    Why don't you try to fit this function with a combination of straight lines?? And why do Fourier series not work?
     
  4. Apr 22, 2016 #3

    mfb

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    A set of straight lines for different ranges should fit best. A Fourier series should give reasonable approximations, but only if you include many terms.
     
  5. Apr 23, 2016 #4

    Svein

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    Looking at the vertical scale: Is your data set really constricted to the value -9.74771?
     
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