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   Mass flow parameter with gamma, r and Mach number as inputs. An
   alternative function is MassFlowParameter which takes cP as an input.
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   Form:
   mFP = MassFlowParameterR( gamma, r, machNo, units )
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   ------
   Inputs
   ------
   gamma      (1,1)   Rate of specific heats
   r          (1,1)   Gas constant
   machNo     (1,:)   Mach number
   units      (1,:)   'eng' or 'mks'

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

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