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

[anonymous]

URL:
  <http://savannah.gnu.org/bugs/?47302>

                 Summary: control system feedback() OR TF() gives wrong result
z plane
                 Project: GNU Octave
            Submitted by: None
            Submitted on: Mon 29 Feb 2016 05:57:00 AM UTC
                Category: Octave Function
                Severity: 3 - Normal
                Priority: 5 - Normal
              Item Group: Incorrect Result
                  Status: None
             Assigned to: None
         Originator Name: Kent Deines
        Originator Email: address@hidden
             Open/Closed: Open
         Discussion Lock: Any
                 Release: 4.0.0
        Operating System: Microsoft Windows

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Details:

I claim no great expertise in control systems, but, my way of thinking is like
this:
the polynomial [0 1]=>z^-1  has a delay of 1 sample, [0 0 1]=>z^-2 has a delay
of 2 samples. [0 1 1]=>z^-1+z^-2 This interpretation is consistent with freqz
and filter.
So
H=tf([ 0 0 1],[1 -1],1);
H(z)=z^-2/(1 -z^-1)
what I get is H(z) = 1/(z-1),\. In fact, shifting the numerator over does
nothing, [0 0 1]=[0 0 0 0 1]


T=feedback(H) adds the numerator and denominator of H to get the denominator
of T. When it does this, it should do it from left to right, not right to
left. Ie adding like delays together.

Maybe my whole way of thinking about his is wrong.

Kent






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