[Octave-bug-tracker] [bug #49433] Bode plot is totally inaccurate

[anonymous]

URL:
  <http://savannah.gnu.org/bugs/?49433>

                 Summary: Bode plot is totally inaccurate
                 Project: GNU Octave
            Submitted by: None
            Submitted on: Tue 25 Oct 2016 01:26:03 AM UTC
                Category: Octave Forge Package
                Severity: 3 - Normal
                Priority: 5 - Normal
              Item Group: Inaccurate Result
                  Status: None
             Assigned to: None
         Originator Name: Jay Ayerson
        Originator Email: address@hidden
             Open/Closed: Open
         Discussion Lock: Any
                 Release: other
        Operating System: Other

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Details:

Using Octave 3.6.4, on fedora core 20.
Octave-control installed 25 October 2016.

Compared bode plot of transfer function (obtained on Matlab) to Octave plot
and found little correlation. Also sketched by hand for reference and found
Octave to be wrong. Both magnitude and angle plots are higher than they should
be in the low frequency region (left side of plot), indicating a systematic
error.

I suspect that either the low-frequency cutoff is being ignored, or the
integrator has been discarded.

The transfer function is entered using
s=tf('s');
and matches the polynomial given by Matlab.

Transfer function:
G=50*(1+s/5)*(1+500*s)/[(1+s/2)*(1+s/30)*(1+s/50)*(1+1000*s)*s];

Is this a version compatibility fault or a software bug?



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File Attachments:


-------------------------------------------------------
Date: Tue 25 Oct 2016 01:26:03 AM UTC  Name: Bode4.PNG  Size: 47kB   By: None
The attached file is the expected result from Matlab.
<http://savannah.gnu.org/bugs/download.php?file_id=38804>

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