bugGNU Octave - Bugs: bug #36521, [octave forge] (signal) buttord...


bug #36521: [octave forge] (signal) buttord function overdesigns

Submitter:  Luke <ltclifton>
Submitted:  Tue 22 May 2012 07:35:35 AM UTC
Category:  Octave Forge Package Severity:  3 - Normal
Priority:  5 - Normal Item Group:  Incorrect Result
Status:  Fixed Assigned to:  None
Originator Name:  Open/Closed:  * Closed
Release:  * dev Operating System:  * Any
* Mandatory Fields

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Wed 04 Apr 2018 01:31:22 AM UTC, comment #3: 

With the improved buttord function in bug #46444, buttord returns the same as SciPy

>> [N, Wn] = buttord ([0.16, 0.24], [0.12, 0.32], 3, 12)
N =  2
Wn =

   1.599611619313067e-01   2.400551981118385e-01

Current versions of Matlab also return N = 2 for this set of constraints.

This bug will be fixed when the work at bug #46444 is integrated.

Mike Miller <mtmiller>
Project Administrator
Thu 24 Nov 2016 12:52:31 AM UTC, comment #2: 

Using signal 1.3.2, I get

[n, Wn] = buttord([0.16 0.24], [0.12 0.32], 3, 12)
warning: buttord: seems to overdesign bandpass and bandreject filters
warning: called from
    buttord at line 60 column 5
n =  3
Wn =

   0.15988   0.24017

If n is the order of the filter (is not mentioned in the help of this function nor of function butter) it seems now the filter is under-designed.

Juan Pablo Carbajal <juanpi>
Project Member
Tue 22 May 2012 11:34:25 AM UTC, comment #1: 

CC'ing OF list

Jordi GutiƩrrez Hermoso <jordigh>
Project Administrator
Tue 22 May 2012 07:35:35 AM UTC, original submission:  

The buttord() function in the signal processing library over designs band pass filters. This seems to be a known issue as an error is printed at run-time. However I could not find a corresponding bug report. I have confirmed that it does over-design by comparing the output to Matlabs equivalent function.

The following example demonstrates

[n, Wn] = buttord([0.16 0.24], [0.12 0.32], 3, 12)

Octave reports that a 6th order filter is required.

Matlab report (correctly) that a 4th order filter is required.

While Octave's solution satisfies the requirements, it is misleading, and buggy behavior to report this solution.

Luke <ltclifton>


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    Follow 11 latest changes.

    Date Changed by Updated Field Previous Value => Replaced by
    2018-04-30 mtmiller StatusConfirmed Fixed
        Open/ClosedOpen Closed
    2018-04-04 mtmiller Dependencies- Depends on bugs #46444
    2017-08-13 jwe Summarysignal package: buttord() overdesigns [octave forge] (signal) buttord function overdesigns
    2013-06-21 mtmiller StatusNone Confirmed
        Release3.6.1 dev
        Summarybuttord() over designs signal package: buttord() overdesigns
    2013-05-16 jwe CategoryNone Octave Forge Package
        StatusOctave Forge None
    2012-05-22 jordigh StatusNone Octave Forge
        Carbon-Copy- Added -email is unavailable-

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