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   Thrust model for a gas turbine engine
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   Form:
   thrust = ACThrust( idl, mil, max, yH, xM, h, m, p )
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   Inputs
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   idl           (alt,mach)  Thrust coefficients for idle power
   mil           (alt,mach)  Military power
   max           (alt,mach)  Max Power
   yH            (alt)       Row coefficient values
   xM            (mach)      Columns of matrices
   h                         Altitude
   m                         Mach number
   p                         Power

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   Outputs
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   thrust                    Thrust

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