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   Computes a pointing budget over n categories. 
   Terms will be RSS'd within categories and categories will be added.
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   Form:
   [cep, r, s, t, cList] = PBudget( errors, desc, categ, aZ, eL, file )
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   ------
   Inputs
   ------
   errors          (n,3)  Error contributions [roll,pitch,yaw] (3 sigma)
   desc            (n)    Descriptions of the error contributions
   categ           (n)    Categories
   aZ                     Azimuth of beam (deg)
   eL                     Elevation of beam (deg)
   file                   File name for printed budget

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   Outputs
   -------
   cep                    Circular error (0.99865)
   r               (2,1)  Azimuth and elevation errors
   s               (m,3)  Summary by category (m = number of categories)
   t               (1,3)  Totals
   cList           (m,:)  Categories corresponding to s

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