FSolarSailAngles:

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   RHS for a Newton solver for sail angles.

   Since version 7.
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   Form:
   f = FSolarSailAngles( x, d )
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   ------
   Inputs
   ------
   x             (2,1)   Sail angles [alpha;beta]
   d             (1,1)   Data structure
                         .rhoEps (1,1) Thermal plus diffuse
                         .rhoS   (1,1) Specular coefficient
                         .rhoDA  (1,1) Diffuse + absorption
                         .e      (3,1) Lambda

   -------
   Outputs
   -------
   x             (:,1)   The solution
   err           (:,1)   The errors
   n             (1,1)   Number of iterations

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