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   Mass flow parameter.
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   Form:
   mFP = MassFlowParameter( gamma, R, machNo, units )
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   ------
   Inputs
   ------
   gamma      (1,1)   Rate of specific heats
   cP         (1,1)   Specific heat
   machNo     (1,:)   Mach number
   units      (1,:)   'eng' or 'mks'

   -------
   Outputs
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   mFP        (1,:)   Mass flow parameter

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