bugGNU Octave - Bugs: bug #55098, [octave forge] (signal) wrong...

 
 

bug #55098: [octave forge] (signal) wrong result from filtic when a(1) != 1

Submitted by:  Tony Richardson <amrichardson>
Submitted on:  Sun 25 Nov 2018 06:55:42 PM UTC  
 
Category:  Octave Forge Package Severity:  3 - Normal
Priority:  5 - Normal Item Group:  Incorrect Result
Status:  Duplicate Assigned to:  None
Originator Name:  Open/Closed:  Closed
Release:  4.4.1 Operating System:  Any

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Thu 06 Dec 2018 07:40:39 PM UTC, comment #2:

Thank you. This was actually reported a year ago by you. Can you please take a look at bug #52254 and post any further information there? Can you provide a patch against filtic.m that I can apply? Thanks.

Mike Miller <mtmiller>
Project Administrator
Sun 25 Nov 2018 07:51:19 PM UTC, comment #1:

Sorry, the normalized example in the original post that is supposed to return the correct result should be:

and not

Tony Richardson <amrichardson>
Sun 25 Nov 2018 06:55:42 PM UTC, original submission:

The filtic function from the signal package gives incorrect results when the first element of the 'a' vector is not equal to 1. Here is a simple example to illustrate the error:

The correct result (and also the result returned by MATLAB) is -0.5.

Octave returns the correct result when the b and a vectors (the first two arguments to filtic) are normalized so that the first element of the a vector is 1:

Theoretically, the result should be the same regardless of the normalization. That is filtic(1/anorm, [2 1]/anorm, 1) should return -0.5000 regardless of the value of anorm (MATLAB does this).

A simple fix is to divide the return vector (zf) by a(1) at the bottom (just before the endfunction line) of the filtic function:

Tony Richardson <amrichardson>

 

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    Follow 4 latest changes.

    Date Changed by Updated Field Previous Value => Replaced by
    2018-12-06 mtmiller StatusNone => Duplicate
        Open/ClosedOpen => Closed
        Dependencies- => Depends on bugs #52254
    2018-11-28 siko1056 Summarywrong result from filtic when a(1) != 1 => [octave forge] (signal) wrong result from filtic when a(1) != 1

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