InterpolateState:

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   Interpolate a planet's state for a given Julian Date.
   Uses the JPL ephemeris files. The returned state is measured from the solar 
   system barycenter and in the Earth equatorial frame.
   Can be initialized with the binary file name by passing empty for the 
   other inputs, then future calls may omit the file name.
   The initialization status can be checked with a single empty input.

   A binary file can be generated from a text file (ex. ascp2000.405) 
   using the tool EphemUtil, available via ftp:
      ftp://ssd.jpl.nasa.gov//pub/eph/export/
   in the folder C-versions/hoffman. You must compile the tool for your
   system.

   Visit http://ssd.jpl.nasa.gov/?planet_eph_export for more information
   about these ephemerides.
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   Form:
   [X, GM] = InterpolateState( target, time, fileName )
   status = InterpolateState( [], [], fileName )
   status = InterpolateState( [] )
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   1. Mercury
   2. Venus
   3. Earth-Moon Barycenter
   4. Mars
   5. Jupiter
   6. Saturn
   7. Uranus
   8. Neptune
   9. Pluto
   10. Geocentric Moon
   11. Sun

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   ------
   Inputs
   ------
   Target    (1,1)       Planet ID
   Time      (1,1)       Julian date (days)
   fileName   (:)        Binary file name if not initialized

   -------
   Outputs
   -------
   X         (6,1)       Planetary state vector, Earth mean equatorial frame
   GM        (1,1)       Corresponding gravitational parameter (km3/s2)

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Children:

Common: Time/Date2JD
Common: Time/JD2000