[Octave-patch-tracker] [patch #9679] control package : additional frequency points to make bode and nyquist plots smoother

[anonymous]

URL:
  <http://savannah.gnu.org/patch/?9679>

                 Summary: control package : additional frequency points to
make bode and nyquist plots smoother
                 Project: GNU Octave
            Submitted by: None
            Submitted on: Sat 18 Aug 2018 10:13:59 AM UTC
                Category: Forge : other
                Priority: 3 - Low
                  Status: None
                 Privacy: Public
             Assigned to: None
        Originator Email: address@hidden
             Open/Closed: Open
         Discussion Lock: Any

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Details:

When bode and nyquist commands are called without giving explicit frequency
values, control package evaluates the frequency response at 500 frequency
points which are log spaced with in the (min, max) range. The package adds the
natural frequency of the poles/zeroes to the above log spaced vector to ensure
the peaks and notches are not missed.
For systems with poles or zeroes with very low damping ratio (close to
imaginary axis), frequency points at closer intervals are necessary near the
frequency of poles/zeros for a smoother plot. Matlab puts closer points near
such frequencies where sharp magnitude or phase change occur.
The submitted patch uses the relation between magnitude or phase with respect
to frequency for second order systems to calculate the frequency points from
'equally' spaced magnitude and phase vectors by inverting the relation.
The improvement is visible in the nyquist plots for systems with poles and
zeros very very close to imaginary axis. The improvement for bode plots are
not so dramatic.



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File Attachments:


-------------------------------------------------------
Date: Sat 18 Aug 2018 10:13:59 AM UTC  Name: bode_freq_pts.patch  Size: 11KiB 
 By: None
modificationtest.m can be used demonstrate the difference in plotting
<http://savannah.gnu.org/patch/download.php?file_id=44805>
-------------------------------------------------------
Date: Sat 18 Aug 2018 10:13:59 AM UTC  Name: modificationtest.m  Size: 2KiB  
By: None
modificationtest.m can be used demonstrate the difference in plotting
<http://savannah.gnu.org/patch/download.php?file_id=44806>

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