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Math Help - Ellipse: extract "minor axis" (b) when given "arc length" and "major axis" (a)

  1. #1
    Member courteous's Avatar
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    Question Ellipse: extract "minor axis" (b) when given "arc length" and "major axis" (a)

    The 1/4 of the ellipse's arc length is known ( 3 in this case) and so is the semi-major axis a . So, for each a that would be plugged in, how would you get b ?

    Here is (the picture of) the equation:

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  2. #2
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    You don't get any "analytic" form for that. That is an example of a general type of integral called (surprize, surprize!) elliptic integrals. They cannot be done "analytically". You would need to do a numerical integration. (I remember, many years ago, seeing 20 large volumes at the University of Florida library giving values for elliptic integrals with different parameters.)
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  3. #3
    Member courteous's Avatar
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    I was looking at (among other methods; I don't really know what I'm doing ) Newton's method ... but, I'm at lost as to how to use it in practice (as in above equation)?

    How would you go about it, which algorithm would you use? Just a rough outline will (I hope) do.
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