RSunECI:

Path: SC/Ephem

% Generate the sun position in the earth-centered inertial frame. 
   Uses SunV1

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   Form:
   r = RSunECI( jD )
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   Inputs
   ------
   jD        (1,:)   Julian date

   -------
   Outputs
   -------
   r         (3,:)   Sun vector

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