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Math Help - Function Constants from Data?

  1. #1
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    Function Constants from Data?

    I have data:

    x = 1.0, y = 1.5
    x = 2.0 y = 0.45
    x = 3.0 y = 0.21111
    x = 4.0, y = 0.121324

    I know this data comes from a function that has 2 or more inverse square functions added to each other. Example...

    y = (A / x^2) + (B / (C + X)^2)

    or

    y = (A / x^2) + (B / (C + X)^2) + (D / (F + X)^2)

    etc....

    How can I solve for the constants when there are two added inverse square functions or more? Any suggestions would be greatly appreciated.

    Thanks in advance,

    David
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  2. #2
    Grand Panjandrum
    Joined
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    Quote Originally Posted by bnvm View Post
    I have data:

    x = 1.0, y = 1.5
    x = 2.0 y = 0.45
    x = 3.0 y = 0.21111
    x = 4.0, y = 0.121324

    I know this data comes from a function that has 2 or more inverse square functions added to each other. Example...

    y = (A / x^2) + (B / (C + X)^2)

    or

    y = (A / x^2) + (B / (C + X)^2) + (D / (F + X)^2)

    etc....

    How can I solve for the constants when there are two added inverse square functions or more? Any suggestions would be greatly appreciated.

    Thanks in advance,

    David
    It is impossible to fit a model with more parameters than there are data points uniquely to the data. It is nearly always possible to find a solution though. I would suggest using the Excel solver.

    The first of your models has only three parameters, so a least squares fit of the model to the data should give a unique solution.

    RonL
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