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   Converts tangential accelerations into radial using equinoctial elements.
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   Form:
   aR = CT2REq( eq, aT, mu )
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   Inputs
   ------
   eq                    Equinoctial elements
   aT                    Tangential vector
   mu                    Gravitational parameter

   -------
   Outputs
   -------
   aR                    Radial vector or transformation matrix

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   References: Battin, R.H., An Introduction to the Methods and Mathematics
                of Astrodynamics, AIAA, New York, 1987, pp. 490.
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