Constraints_Structure:

--------------------------------------------------------------------------
   Initialize a constraints data structure.

   Since version 7.
--------------------------------------------------------------------------
   Form:
   c = Constraints_Structure( nU );
--------------------------------------------------------------------------

   ------
   Inputs
   ------
   nU           (1)    Number of unique states = # of structures to generate

   -------
   Outputs
   -------
   c            (.)    Constraints data structure with fields:
                          - variable
                          - nRestrict
                          - restrictID
                          - nDuplicates
                          - phase

--------------------------------------------------------------------------