[Octave-bug-tracker] [bug #53164] Incorrect Nyquist plot

[anonymous]

URL:
  <http://savannah.gnu.org/bugs/?53164>

                 Summary: Incorrect Nyquist plot
                 Project: GNU Octave
            Submitted by: None
            Submitted on: Thu 15 Feb 2018 02:52:24 PM UTC
                Category: Plotting
                Severity: 3 - Normal
                Priority: 5 - Normal
              Item Group: Incorrect Result
                  Status: None
             Assigned to: None
         Originator Name: Tomasz Sokolowski
        Originator Email: address@hidden
             Open/Closed: Open
         Discussion Lock: Any
                 Release: 4.2.1
        Operating System: Microsoft Windows

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Details:

I tried to get Nyquist plot of a system descripted with equation:
0.5/(s*(1+s)^2)
I tried it on locally installed Octave and Octave online with same results.
The code I used is:

octave:1> s=tf('s')
octave:2> sys=1/(s*(s+1)^2)
octave:3> nyquist(sys)

I tried also "sys=tf([1],[1 2 1 0])" but with the same result.
In the attachment there is the result from Octave. Here is the correct result
from wolfram alpha:
https://www.wolframalpha.com/input/?i=nyquist+(0.5%2F(s*(1%2Bs)%5E2))



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File Attachments:


-------------------------------------------------------
Date: Thu 15 Feb 2018 02:52:24 PM UTC  Name: octave-online-line-5.png  Size:
32KiB   By: None

<http://savannah.gnu.org/bugs/download.php?file_id=43328>

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