CFract:

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   Computes the value of a continued fraction of the form
              a0
              ----------------------
              b0 - a1
                   -----------------
                   b1 - a2
                        ------------
                        b2 - a3
                             -------
                             b3

   The maximum accuracy depends on the size of a and b. tol is only
   used for early termination of the series.

   Since version 1.
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   Form:
   x = CFract( a, b, tol )
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   ------
   Inputs
   ------
   a                     a array
   b                     b array
   tol                   Error tolerance

   -------
   Outputs
   -------
   x                     value of fraction

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     References: Battin, R. H., An Introduction to the Mathematics and
                 Methods of Astrodynamics, AIAA, 1987, pp. 67-68.
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