[Octave-bug-tracker] [bug #47302] control system feedback() OR TF() gives wrong result z plane

[Mike Miller]

Update of bug #47302 (project octave):

                  Status:                    None => Wont Fix               
             Open/Closed:                    Open => Closed                 

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Follow-up Comment #2:

This is the correct behavior of the control package functions, not a bug. The
documentation could use some expanding or examples showing how to define
different types of systems.

The easiest way to get what you want:


H = tf ([0 0 1], [1 -1 0], 1, "tfvar", "z^-1")

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

        z^-2  
 y1:  --------
      1 - z^-1

Sampling time: 1 s
Discrete-time model.


The control functions use positive powers of the variable z by default,
whereas DSP people like to think in terms of negative powers of z, which you
have to explicitly request as shown above (and also make sure the num and den
vectors align).

If you try the above and something else doesn't work the way you expect,
please file another bug report.

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