[bug #68195] Incorrect Bode plots with ILL-conditioned systems

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URL:
  <https://savannah.gnu.org/bugs/?68195>

                 Summary: Incorrect Bode plots with ILL-conditioned systems
                   Group: GNU Octave
               Submitter: luiz
               Submitted: Mon 30 Mar 2026 01:19:37 PM UTC
                Category: None
                Severity: 3 - Normal
                Priority: 5 - Normal
              Item Group: Incorrect Result
                  Status: None
             Assigned to: None
         Originator Name: Luiz Antonio Maccari Jr.
        Originator Email:
             Open/Closed: Open
         Discussion Lock: Unlocked
                 Release: 11.1.0
        Operating System: Any
           Fixed Release: None
         Planned Release: None


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Follow-up Comments:


-------------------------------------------------------
Date: Mon 30 Mar 2026 01:19:37 PM UTC By: Luiz Antonio Maccari Junior <luiz>
Hi,

I am working with ill-condioned systems. And the bode plots are being plotted
with a strange noise. In order to reproduce it I am providing the annexed
"octave.mat" file and using the following code:


load('octave')

freq=[1:10:10e4];

figure
bode(So_LQG,freq)

figure
bode(So_KF,freq)


The bode plot I getting in Octave is:

fig1.png

However, with MATLAB the bode plot is more coherent and seems to be correct as
can be seen in 

Figure_3.png

Best regards.







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File Attachments:

Name: octave.mat                     Size: 1.2KiB
    <https://file.savannah.gnu.org/file/octave.mat?file_id=58412>

Name: Figure_3.png                   Size: 54KiB
    <https://file.savannah.gnu.org/file/Figure_3.png?file_id=58413>

Name: fig1.png                       Size: 59KiB
    <https://file.savannah.gnu.org/file/fig1.png?file_id=58414>



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