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   Aborptivity and emissivity of a gray body.
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   Form:
    [alpha, epsilon] = GrayBody( alphaOrEpsilon )
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   ------
   Inputs
   ------
   alphaOrEpsilon  (1,:) Either alpha or epsilon

   -------
   Outputs
   -------
   alpha           (1,:) Absorptivity
   epsilon         (1,:) Emissivity

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