bugGNU Octave - Bugs: bug #48138, control package: impulse function...

 
 

bug #48138: control package: impulse function scales impulse response incorrectly

Submitted by:  Jose Andrade <joseandrade>
Submitted on:  Sun 05 Jun 2016 07:06:41 PM UTC  
 
Category: Octave Forge PackageSeverity: 3 - Normal
Priority: 5 - NormalItem Group: Regression
Status: DuplicateAssigned to: None
Originator Name: Jose AndradeOpen/Closed: Closed
Release: 4.0.2Operating System: Any

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Sun 05 Jun 2016 09:16:06 PM UTC, comment #5:

Thanks, I'll close this as a duplicate then. Please post any new information or patches on bug #46597.

Mike Miller <mtmiller>
Project Administrator
Sun 05 Jun 2016 09:14:40 PM UTC, comment #4:

I rewrote the posted script (and quoted in a verbatim block) to make it clearer what the computed parameters are:

I can also confirm that this works correctly in control version 2.8.5 but not in 3.0.0.

With version 3.0.0, if I scale the impulse response by the sampling period, I get something that more closely agrees with the correct result, especially as dt is made smaller.

Mike Miller <mtmiller>
Project Administrator
Sun 05 Jun 2016 09:13:39 PM UTC, comment #3:

Mike I think it is.

Doug Stewart <dastew>
Sun 05 Jun 2016 09:12:06 PM UTC, comment #2:

Doug, is this the same issue as bug #46597 that you were looking at earlier?

Mike Miller <mtmiller>
Project Administrator
Sun 05 Jun 2016 09:08:17 PM UTC, comment #1:

Yes there is a problem.
The C2D function does not have an impulse invariant
method, so the program for the impulse response
uses the ZOH method, which is wrong.

I started making an impulse invariant method for the C2D but got bogged down on the multiple repeated roots part. I will now prod
myself and get working on it.

I would be easy to do if the control pkg would allow complex numerators and denominators but it doesn't. So I am writing
a lot of code to handle these repeated roots.

After the C2D is upgraded then it will be easy to get the impulse function working.
Doug

Doug Stewart <dastew>
Sun 05 Jun 2016 07:06:41 PM UTC, original submission:

There is a bug on the Impulse function of the Control Package.

The Exemple code:

t=0:0.1:30;
NUM=[0.9375]; DEN=[1 2 4];
sys=tf(NUM,DEN)
yi=impulse(sys,t);
yii=exp(-t).(0.5412sin(1.7321*t));
figure
plot(t,yi,t,yii)
title('Impulse Response of LTI System')

The correct answer should be the same graph, but they are different.

Jose Andrade <joseandrade>

 

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    Follow 9 latest changes.

    Date Changed By Updated Field Previous Value => Replaced By
    Sun 05 Jun 2016 09:16:06 PM UTCmtmillerStatusConfirmed=>Duplicate
      Open/ClosedOpen=>Closed
      Dependencies-=>Depends on bugs #46597
    Sun 05 Jun 2016 09:14:40 PM UTCmtmillerItem GroupIncorrect Result=>Regression
      StatusNone=>Confirmed
      Operating SystemMicrosoft Windows=>Any
      SummaryImpulse function of the Control Package=>control package: impulse function scales impulse response incorrectly
    Sun 05 Jun 2016 07:06:41 PM UTCjoseandradeAttached File-=>Added Impulse Response of LTI System.pdf, #37399
      Carbon-Copy-=>Added -unavailable-

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