[Octave-bug-tracker] [bug #62185] Function 'impulse' throws error for a certain simple 'ss' system

[anonymous]

URL:
  <https://savannah.gnu.org/bugs/?62185>

                 Summary: Function 'impulse' throws error for a certain simple
'ss' system
                 Project: GNU Octave
            Submitted by: None
            Submitted on: Tue 15 Mar 2022 02:40:39 AM UTC
                Category: Octave Forge Package
                Severity: 3 - Normal
                Priority: 5 - Normal
              Item Group: Incorrect Result
                  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:

The function 'impulse' throws an error when computing the impulse response of
a second order state-space model. Here is the relevant code:


% Initialization

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))


The third impulse response fails to produce an output and throws the following
error:


error: Order numerator >= order denominator
error: called from
    imp_invar at line 95 column 5
    __c2d__ at line 65 column 16
    c2d at line 87 column 7
    __time_response__ at line 134 column 13
    impulse at line 79 column 13
    mass_spring_damper_ss_demo_01 at line 51 column 1
>>


For reference, Matlab (version info below) is able to compute the same impulse
response without crashing.


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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