FFEccDX:

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   Compute the first derivative of x with respect to true anomaly.
   This is used by the FFEccXExt function.

   Since version 7.
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   Form:
   dx = FFEccDX( nu, e, D, dH );
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   ------
   Inputs
   ------
   nu               (1)   True anomaly [rad]
   e                (1)   Eccentricity
   D               (6,1)  Integration constants computed from i.c.'s
   dH               (1)   Integration constant computed from H(nu0)=0

   -------
   Outputs
   -------
   dx               (1)   First derivative of x with respect to true anomaly

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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/FFEccRMat