[Octave-bug-tracker] [bug #63052] [octave forge] (control) Inverse operation with transfer function variables resulting in wrong results

[Nicholas Jankowski]

Update of bug #63052 (project octave):

                  Status:                    None => Need Info              
                 Summary: (Control) Inverse operation with transfer function
variables resulting in wrong results => [octave forge] (control) Inverse
operation with transfer function variables resulting in wrong results

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Follow-up Comment #4:

what control and signal package versions did you have installed on each
system?

here's what I get with Matlab 2022a:


FT =
 
  2 s^9 + 49 s^8 + 1359 s^7 + 2.025e04 s^6 + 274280 s^5 + 2.603e06 s^4 +
1.933e07 s^3 + 1.06e08 s^2 + 3.263e08 s + 3.97e08
 
------------------------------------------------------------------------------------------------------------------------
     s^9 + 24 s^8 + 663 s^7 + 9788 s^6 + 131931 s^5 + 1.249e06 s^4 + 9.25e06
s^3 + 5.096e07 s^2 + 1.584e08 s + 1.951e08
 
Continuous-time transfer function.


FT =
 
  2 s^9 + 49 s^8 + 1359 s^7 + 2.025e04 s^6 + 2.743e05 s^5 + 2.603e06 s^4 +
1.933e07 s^3 + 1.06e08 s^2 + 3.262e08 s + 3.97e08
 
--------------------------------------------------------------------------------------------------------------------------
     s^9 + 24 s^8 + 663 s^7 + 9788 s^6 + 1.319e05 s^5 + 1.249e06 s^4 + 9.25e06
s^3 + 5.096e07 s^2 + 1.584e08 s + 1.951e08
 
Continuous-time transfer function.


FT2 =
 
  2 s^3 + 17 s^2 + 331 s + 1180
  -----------------------------
    s^3 + 8 s^2 + 157 s + 580
 
Continuous-time transfer function.


and on my Windows 10, Octave 7.2.0, control 3.4.0, signal 1.4.2:

>> FT = C*inv(s*eye(3)-A)*B+D
warning: tf: converting to minimal state-space for MIMO TF interconnections
warning: called from
    __sys_connect__ at line 103 column 5
    mtimes at line 58 column 7

warning: tf: converting to minimal state-space for MIMO TF interconnections
warning: called from
    __sys_connect__ at line 103 column 5
    mtimes at line 58 column 7
    minus at line 45 column 7

warning: tf: converting to minimal state-space for MIMO TF interconnections
warning: called from
    __sys_connect__ at line 103 column 5
    mtimes at line 58 column 7
    minus at line 45 column 7

warning: tf: converting to minimal state-space for MIMO TF interconnections
warning: called from
    __sys_connect__ at line 103 column 5
    mtimes at line 58 column 7

warning: tf: converting to minimal state-space for MIMO TF interconnections
warning: called from
    __sys_connect__ at line 103 column 5
    mtimes at line 58 column 7


Transfer function 'FT' from input 'u1' to output ...

      2 s^2 + 80.76 s + 291
 y1:  ---------------------
      s^2 + 38.66 s + 142.5

Continuous-time model.
>> FT= minreal (FT)

Transfer function 'FT' from input 'u1' to output ...

      2 s^2 + 80.76 s + 291
 y1:  ---------------------
      s^2 + 38.66 s + 142.5

Continuous-time model.
>> [num,den] =ss2tf (A,B,C,D);
>> FT2 = tf (num,den)

Transfer function 'FT2' from input 'u1' to output ...

      2 s^3 + 17 s^2 + 331 s + 1180
 y1:  -----------------------------
        s^3 + 8 s^2 + 157 s + 580

Continuous-time model.
-verbatm-


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