State_Structure:

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   Initialize a state data structure.

   Since version 7.
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   Form:
   state = State_Structure( n );
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   ------
   Inputs
   ------
   none

   -------
   Outputs
   -------
   state        (.)    State data structure with fields:
                          - el     Standard elements [a,i,W,w,e,M]
                          - elA    Alfriend elements [a,theta,i,q1,q2,W]
                          - dEl    Alfriend element differences
                          - xH     Hills-frame relative state [km;km/s]
                          - mass   Mass [kg]
                          - tM     Measurement epoch [sec]

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