patchGNU Octave - Patches: patch #10352, [octave forge] (signal) adding...

 
 

patch #10352: [octave forge] (signal) adding islinphase.m

Submitter:  Leonardo <leolca>
Submitted:  Thu 25 May 2023 05:26:54 PM UTC
   
 
Category:  Forge : new function Priority:  5 - Normal
Status:  Need Info Privacy:  Public
Assigned to:  None Open/Closed:  Open
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Sun 16 Jul 2023 12:01:01 PM UTC, comment #7: 

Afaict, `islinphase` is part of the Signal Processing Toolbox of the MathWorks. The closest match for Octave would probably be the "signal" package.

Adding its maintainer to the CC-list of this report.

Markus Mützel <mmuetzel>
Group administrator
Thu 29 Jun 2023 12:36:15 PM UTC, comment #6: 

It looks like grpdelay in octave accepts different arguments than the matlab version

John Donoghue <lostbard>
Group Member
Wed 28 Jun 2023 05:13:38 PM UTC, comment #5: 

Once again,

For the filter defined by b = [1 -1]; a = [1 -2]; the angle will be:

arg((1 - e^(-j ω))/(1 - 2 e^(-j ω)))

and the group delay will be:

d/dω(arg((1 - e^(-j ω))/(1 - 2 e^(-j ω)))) = (π j e^(j ω) δ((-1 + e^(j ω))/(-2 + e^(j ω))))/(e^(j ω) - 2)^2

and we may conclude that there is a discontinuity at ω = 0

reference:
https://www.wolframalpha.com/input?i=angle+%28+%281+-+e%5E%28-j%CF%89%29%29+%2F+%281+-+2e%5E%28-j%CF%89%29%29+%29

Leonardo <leolca>
Wed 28 Jun 2023 05:06:15 PM UTC, comment #4: 

I guess the problem with this filter is that at ω = 0 we have undefined or indeterminate angle.

H(0) = (1 - e^(-j 0)) / (1 - 2e^(-j 0)) = 0 / (-1)

arg(0) = ?

In another approach, the numerator might be expressed by:
B(ω) = e^(-jω/2)(e^(jω/2) - e^(-jω/2)) = e^(-jω/2)(2j sin(ω/2))
arg(B(ω)) = -ω/2 + angle(2j sin(ω/2))

and the denominator by:
A(ω) = e^(-jω/2)(3jsin(ω/2) - cos(ω/2))
ang(A(ω)) = -ω/2 + arctan((3sin(ω/2)) / (-cos(ω/2)))

angle(H(ω)) = angle(2j sin(ω/2)) - arctan((3sin(ω/2)) / (-cos(ω/2)))

for ω > 0
angle(H(ω)) = π/2 - arctan((3sin(ω/2)) / (-cos(ω/2)))

for ω = 0 it is undefined.

That is causing the warning.

Here is the compared result of grpdelay in GNU Octave and Matlab for that particular filter:

GNU Octave
octave:1> pkg load signal
octave:2> b = [1 -1]; a = [1 -2];
octave:3> [gd, w] = grpdelay (b, a);
octave:4> [gd(1:10)'; w(1:10)']
ans =

  -1.0000  -1.4999  -1.4995  -1.4990  -1.4982  -1.4972  -1.4959  -1.4945  -1.4928  -1.4909
        0   0.0061   0.0123   0.0184   0.0245   0.0307   0.0368   0.0430   0.0491   0.0552


MATLAB

>> b = [1 -1]; a = [1 -2];
>> [gd, w] = grpdelay (b, a);
>> [gd(1:10)'; w(1:10)']


ans =

   -1.5000   -1.4999   -1.4995   -1.4990   -1.4982   -1.4972   -1.4959   -1.4945   -1.4928   -1.4909
         0    0.0061    0.0123    0.0184    0.0245    0.0307    0.0368    0.0430    0.0491    0.0552


Maybe we should point this to Paul Kienzle and Julius O. Smith III who have created the grpdelay.m function in GNU Octave.

To avoid this warning in the tests, we could just remove this one.

Leonardo <leolca>
Wed 28 Jun 2023 01:32:02 PM UTC, comment #3: 

I diffed the attached grpdelay to mine and its the same, I also verified islinphase is the same as the attached file.

Removing the ';' on the polebins  = find (abs (den) < minmag) line in grpdelay and running I see:

> b = [1 -1]; a = [1 -2];

f = islinphase (b, a, 1E-1);
polebins = 1
warning: grpdelay: setting group delay to 0 at singularity
warning: called from
    grpdelay at line 191 column 5
    islinphase at line 94 column 9




John Donoghue <lostbard>
Group Member
Wed 28 Jun 2023 12:55:06 PM UTC, comment #2: 

I had no warning here.

'grpdelay' is a function from the file /usr/share/octave/packages/signal-1.4.3/grpdelay.m

The function grpdelay.m used follows attached.

(file #54891)

Leonardo <leolca>
Tue 27 Jun 2023 03:12:02 PM UTC, comment #1: 

Some of the tests give warnings:


b = [1 -1]; a = [1 -2];
f = islinphase (b, a, 1E-1);
warning: grpdelay: setting group delay to 0 at singularity
warning: called from
    grpdelay at line 191 column 5
    islinphase at line 96 column 10


John Donoghue <lostbard>
Group Member
Thu 25 May 2023 05:26:54 PM UTC, original submission:  

Implementation of the function islinphase.

Leonardo <leolca>

 

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

Attach Files:
   
   
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Attached Files
file #54891:  grpdelay.m added by leolca (12KiB - text/x-objcsrc)
file #54782:  islinphase.patch added by leolca (5KiB - text/x-patch)
file #54783:  islinphase.m added by leolca (5KiB - text/x-objcsrc)

 

Depends on the following items: None found

Items that depend on this one: None found

 

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    Follow 7 latest changes.

    Date Changed by Updated Field Previous Value => Replaced by
    2023-07-16 mmuetzel CategoryCore : new function Forge : new function
        Summaryadding islinphase.m [octave forge] (signal) adding islinphase.m
        Carbon-Copy- Added mtmiller
    2023-06-28 leolca Attached File- Added grpdelay.m, #54891
    2023-06-27 lostbard StatusNone Need Info
    2023-05-25 leolca Attached File- Added islinphase.patch, #54782
        Attached File- Added islinphase.m, #54783

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