VarEqSailPlanet:

--------------------------------------------------------------------------
   Sail variational equations in state space form for a planet-centered orbit.

   Since version 7.
--------------------------------------------------------------------------
   Form:
   M = VarEqSailPlanet( rho, z, omega )
--------------------------------------------------------------------------

   ------
   Inputs
   ------
   rho     (1,1)    Amplitude
   z       (1,1)    Anti-sun displacement
   omega   (1,1)    Orbit rate

   -------
   Outputs
   -------
   M       (2,2)    Dynamics matrix

--------------------------------------------------------------------------
   Reference: Colin R. McInnes, "Solar Sailing: Technology, Dynamics and Mission
              Applications", Springer Praxis, London, 1999. p. 204
--------------------------------------------------------------------------