[Octave-bug-tracker] [bug #62186] Function 'bode' produces possibly correct but mis-presented result

[anonymous]

URL:
  <https://savannah.gnu.org/bugs/?62186>

                 Summary: Function 'bode' produces possibly correct but
mis-presented result
                 Project: GNU Octave
            Submitted by: None
            Submitted on: Tue 15 Mar 2022 03:01:47 AM UTC
                Category: Octave Forge Package
                Severity: 3 - Normal
                Priority: 5 - Normal
              Item Group: None
                  Status: None
             Assigned to: None
         Originator Name: Chris
        Originator Email: ccarter@tmt.org
             Open/Closed: Open
                 Release: 6.4.0
         Discussion Lock: Any
        Operating System: Microsoft Windows

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Details:

For the second order state-space system below, function 'bode' produces an
incorrectly presented plot, i.e. the X-axis lower limit is much lower than
necessary and the lower bound of the plot is shown with no data points present
at lower frequencies. See attached image.


m = 1.0     % Mass
k = 10.0    % Spring constant
b = 1      % Damping constant

% State-space model of the mass-spring-damper system

A = [0 1;...
     -k/m -b/m]
     
B = [0;...
    -1/m]
    
C = [1 0;...
     0 1;...
     -k/m -b/m]

D = [0;
     0;
     -1/m]

states = {'Position' 'Velocity'}
inputs = {'Force'}
outputs = {'Position' 'Velocity' 'Acceleration'}

system = ss(A,B,C,D,'statename',states,...
'inputname', inputs,...
'outputname', outputs)

% Time-domain responses

% Impulse responses

figure()
impulse(system(1,1))

figure()
impulse(system(2,1))

% figure()
% impulse(system(3,1))

% Step responses

figure()
step(system(1,1))

figure()
step(system(2,1))

figure()
step(system(3,1))

% Pole-zero maps

figure()
pzmap(system(1,1))

% Bode plot

figure()
bode(system(1,1));  % Force to Position
title('Bode: Force to Position')

figure()
bode(system(2,1));  % Force to Velocity
title('Bode: Force to Velocity')

figure()
bode(system(3,1));  % Force to Acceleration
title('Bode: Force to Acceleration')


Matlab (version info below) is able to produce a properly scaled plot (see
attached image).


MATLAB Version: 9.11.0.1687835 (R2021b) Prerelease
MATLAB License Number: 865865
Operating System: Microsoft Windows 10 Pro Version 10.0 (Build 19044)
Java Version: Java 1.8.0_202-b08 with Oracle Corporation Java HotSpot(TM)
64-Bit Server VM mixed mode




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File Attachments:


-------------------------------------------------------
Date: Tue 15 Mar 2022 03:01:47 AM UTC  Name: Octave@Bode.PNG  Size: 344KiB  
By: None

<http://savannah.gnu.org/bugs/download.php?file_id=52988>
-------------------------------------------------------
Date: Tue 15 Mar 2022 03:01:47 AM UTC  Name: Matlab@Bode.PNG  Size: 124KiB  
By: None

<http://savannah.gnu.org/bugs/download.php?file_id=52989>

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