Osc2Mean:

--------------------------------------------------------------------------
   Transforms osculating orbital elements to mean orbital elements.

   Since version 7.
--------------------------------------------------------------------------
   Form:
   el_mean = Osc2Mean(el_osc,J2);
--------------------------------------------------------------------------

   ------
   Inputs
   ------
   el_osc           (1,6)    osculating orbital elements
   J2               (1,1)    Magnitude of J2 term

   -------
   Outputs
   -------
   el_mean          (1,6)    mean orbital elements

--------------------------------------------------------------------------
  References:  Terry Alfriend, Texas A&M University
--------------------------------------------------------------------------