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   Computes a collinear Lagrange point. Default is for the earth/moon
   system.
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   Form:
   rL = RLagrange( rS, mR, lPoint )
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   ------
   Inputs
   ------
   rS          (3,1)  R of the secondary
   mR          (1,1)  Mass secondary/mass primary
   lPoint      (1,1)  Desired Lagrange point

   -------
   Outputs
   -------
   rL          (3,1)  Lagrange coordinates

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