FFEccDMatPeriodic:

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   Given an initial Hills state (xH0) at a particular true anomaly (nu0)
   of an eccentric orbit (e), compute the in-plane velocities (dx and dy) 
   required for periodic motion.

   Use any of the following methods:
     1) symmetric              - Motion is symmetric in-track about the origin
     2) fuel optimized         - Use LP to find minimum of abs(dx) + abs(dy)
     3) velocity constraint    - Leave dx = dx0, solve for new dy

   Since version 7.
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   Form:
   [D, dx, dy] = FFEccDMatPeriodic( xH0, nu0, e, method );
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   ------
   Inputs
   ------
   xH0             (6,1)  Initial state in Hills frame
   nu0              (1)   True anomaly (at initial state) [rad]
   e                (1)   Eccentricity
   method           (1)   Indicate which method to use
                             1 - symmetric 
                             2 - fuel optimization
                             3 - velocity constraint
   -------
   Outputs
   -------
   D               (6,1)  Vector of integration constants
   dx               (1)   Scaled radial velocity required for periodic motion
   dy               (1)   Scaled along-track velocity required for periodic motion

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   References: Inalhan, Tillerson, How, "Relative Dynamics and Control of
   Spacecraft Formations in Eccentric Orbits", Journal of Guidance,
   Control & Dynamics, Vol.25, No.1, Jan-Feb 2002.
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	  Copyright 2004 Princeton Satellite Systems, Inc.
   All rights reserved.
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Children:

FormationFlying: EccDynamics/FFEccDH
FormationFlying: EccDynamics/FFEccRMat