Geometry_Structure:

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   Initialize a geometry data structure.

   Since version 7.
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   Form:
   g = Geometry_Structure( nU );
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   ------
   Inputs
   ------
   nU           (1)    Number of geometry structures = # of unique states

   -------
   Outputs
   -------
   g            (.)    Geometry data structure with fields:
                          - y0
                          - aE
                          - beta
                          - zInc
                          - zLan

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