MuFermenter:

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   Computes the specific growth rate of a fermenter.
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   Form:
   mu = MuFermenter( x, d )
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   ------
   Inputs
   ------
   x           (4,1) State [CA1;T1;CA2;T2]
   d           (1,1) data structure
                     .yXS      (1,1)   Cell-mass yield parameter
                     .beta     (1,1)   Yeild parameter
                     .pM       (1,1)   Constant parameter
                     .kI       (1,1)   Constant parameter
                     .sF       (1,1)   Dilution rate
                     .d        (1,1)   Yield parameter
                     .alpha    (1,1)   Maximum specific growth rate
                     .muM      (1,1)   Constant parameter
                     .kM       (1,1)   Feed substrate concentration
   -------
   Outputs
   -------
   mu          (3,1) State derivative

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   Reference: Henson, M. A. and D. E. Seborg. (1997.) Nonlinear 
              Process Control, Prentice-Hall. pp. 203-204.
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