bugGNU Octave - Bugs: bug #49318, [octave forge] (signal)...

 
 

bug #49318: [octave forge] (signal) butter/cheby1/cheby2/ellip return zeros and poles as row vectors

Submitted by:  Yuzhou Cheng <yc2986>
Submitted on:  Tue 11 Oct 2016 09:27:51 PM UTC  
 
Category: Octave Forge PackageSeverity: 2 - Minor
Priority: 5 - NormalItem Group: Incorrect Result
Status: ConfirmedAssigned to: None
Originator Name: Open/Closed: Open
Release: devOperating System: Any

Add a New Comment(Rich Markup)
   

You are not logged in

Please log in, so followups can be emailed to you.

 

Thu 05 Jan 2017 08:42:46 PM UTC, comment #3:

patches posted to bug #49990 make outputs of butter, cheby1, cheby2 and ellip follow matlab convention. That should address the ellip issue mentioned in comment #2.

Nicholas Jankowski <nrjank>
Wed 12 Oct 2016 02:38:57 AM UTC, comment #2:

Thanks for your bug report. The bug actually appears to be in the way the zeros and poles are returned from the ellip function, not in the zplane function.

Please try zplane again with the vectors transposed, as in:

An easy workaround is to ensure that your zeros and poles vectors are always column vectors.

The unfortunate interface for the zplane function is that if it is given two row vectors, they are taken to be numerator and denominator filter coefficients, column vectors are taken to be zeros and poles. So in this case, ellip appears to be returning row vectors when the user asks for zeros and poles.

Mike Miller <mtmiller>
Project Administrator
Tue 11 Oct 2016 09:49:19 PM UTC, comment #1:

zplane is in the Octave Forge package signal. Changing the Category to Octave Forge Package.

Rik <rik5>
Project Administrator
Tue 11 Oct 2016 09:27:51 PM UTC, original submission:

Matlab version of zplane: https://www.mathworks.com/help/signal/ref/zplane.html

Tested in Octave 4.0.3 using Matlab's example of ellip filter

zplane in Octave generate pole out of unit circle...

According to this thread: http://octave.1599824.n4.nabble.com/Stable-poles-handed-to-quot-filter-quot-can-result-in-unstable-filter-td4634447.html

Probably Octave is calculating Poles using:

Which generate this bug. The correct pole should be just:

By the way, the freqz function plot unstable filter magnitude response for butter. I think maybe it is due to this issue as well.

Yuzhou Cheng <yc2986>

 

(Note: upload size limit is set to 16384 kB, after insertion of the required escape characters.)

Attach File(s):
   
   
Comment:
   

No files currently attached

 

Depends on the following items: None found

Digest:
   bug dependencies.

 

Carbon-Copy List
  • -unavailable- added by jwe (Updated the item)
  • -unavailable- added by nrjank (Posted a comment)
  • -unavailable- added by mtmiller (Posted a comment)
  • -unavailable- added by yc2986 (Submitted the item)
  • -unavailable- added by yc2986
  •  

    Do you think this task is very important?
    If so, you can click here to add your encouragement to it.
    This task has 0 encouragements so far.

    Only project members can vote.

     

    Please enter the title of George Orwell's famous dystopian book (it's a date):

     

     

    Follow 11 latest changes.

    Date Changed By Updated Field Previous Value => Replaced By
    Sun 13 Aug 2017 01:17:01 PM UTCjweSummarysignal package: butter/cheby1/cheby2/ellip return zeros and poles as row vectors=>[octave forge] (signal) butter/cheby1/cheby2/ellip return zeros and poles as row vectors
    Thu 05 Jan 2017 06:31:45 PM UTCmtmillerSummarysignal package: ellip returns zeros and poles as row vectors=>signal package: butter/cheby1/cheby2/ellip return zeros and poles as row vectors
    Thu 05 Jan 2017 06:29:22 PM UTCmtmillerDependencies-=>bugs #49989 is dependent
    Wed 12 Oct 2016 02:38:57 AM UTCmtmillerSeverity3 - Normal=>2 - Minor
      StatusNone=>Confirmed
      Release4.0.3=>dev
      Operating SystemMicrosoft Windows=>Any
      SummarySignal Pack zplane generate wrong zero-pole plot=>signal package: ellip returns zeros and poles as row vectors
    Tue 11 Oct 2016 09:49:33 PM UTCrik5Carbon-CopyRemoved 72865=>-
    Tue 11 Oct 2016 09:49:19 PM UTCrik5CategoryOctave Function=>Octave Forge Package
    Tue 11 Oct 2016 09:27:51 PM UTCyc2986Carbon-Copy-=>Added -unavailable-

    Back to the top


    Powered by Savane 3.1-cleanup1