bugGNU Octave - Bugs: bug #63094, FFT2 produces a result that...

 
 

bug #63094: FFT2 produces a result that differs from MATLAB

Submitter:  None
Submitted:  Fri 23 Sep 2022 12:15:38 PM UTC
 
Category:  Octave Function Severity:  3 - Normal
Priority:  5 - Normal Item Group:  Incorrect Result
Status:  Works For Me Assigned to:  None
Originator Name:  STEPHEN E RANKIN Originator Email:  -email is unavailable-
Open/Closed:  * Closed Release:  * 6.4.0
Operating System:  * GNU/Linux Fixed Release:  None
Planned Release:  None
* Mandatory Fields

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Sun 02 Oct 2022 12:28:46 AM UTC, comment #4: 

No response in a week. Closing as Works for me.

@OP: If it's a bug in Octave it can be reopened. If you need help with your code not working as intended, try https://octave.discourse.group

Arun Giridhar <arungiridhar>
Project Member
Sat 24 Sep 2022 09:27:24 AM UTC, comment #3: 

Which version of the fftw libraries are you using?
What does `version -fftw` return for you?

Markus M├╝tzel <mmuetzel>
Project Member
Fri 23 Sep 2022 06:59:49 PM UTC, comment #2: 

The code works for me on both Octave 6.4.0 and Octave 8, in addition to dasergatskov's 7.2.0. I get the same figure. Marking as Works for me.

@OP: Are you using Qt for graphics or something else? Does it make a difference if you disable hardware rendering before starting Octave?

Arun Giridhar <arungiridhar>
Project Member
Fri 23 Sep 2022 12:34:38 PM UTC, comment #1: 

It works on my octave 7.2 (on linux).

(See attached)

Dmitri.


Dmitri A. Sergatskov <dasergatskov>
Fri 23 Sep 2022 12:15:38 PM UTC, original submission:  

The result of trying to differentiate a Gaussian by FFT fails on Octave running on Ubuntu 22.04, but works on MATLAB with the same code:

    size2 = 101;
    A = 10;
    sigma = 10;
    gauss = zeros(size2);

    for y = 1:size2
        for x = 1:size2
            gauss(y,x)=A*exp(-1/(sigma^2)*((y-size2/2)^2+(x-
            size2/2)^2)); %gaussiana
        end
    end

    hf = fftshift(fft2(gauss));
    [U,V] = meshgrid(-50:50, -50:50);
    hf2 = (exp(1i*2*pi*U/101) - 1).*(exp(1i*2*pi*V/101) - 1).*hf;
    out_freq = real(ifft2(ifftshift(hf2)));
    out_freq = out_freq(1:end-1,1:end-1);
    out_spatial = diff(diff(gauss, 1, 1), 1, 2);
    figure;
    subplot(1,2,1);
    imshow(out_spatial, []);
    title('Derivative from spatial domain');
    subplot(1,2,2);
    imshow(out_freq, []);
    title('Derivative from frequency domain');

Anonymous

 

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Attached Files
file #53745:  fft2_octave72.png added by dasergatskov (19KiB - image/png)
file #53743:  octave.jpg added by None (19KiB - image/jpeg)
file #53744:  matlab.jpg added by None (15KiB - image/jpeg)

 

Depends on the following items: None found

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   bug dependencies.

 

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  • -email is unavailable- added by mmuetzel (Posted a comment)
  • -email is unavailable- added by arungiridhar (Posted a comment)
  • -email is unavailable- added by dasergatskov (Updated the item)
  • -email is unavailable- added by None (Submitted the item)
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    Follow 6 latest changes.

    Date Changed by Updated Field Previous Value => Replaced by
    2022-10-02 arungiridhar Open/ClosedOpen Closed
    2022-09-23 arungiridhar StatusNone Works For Me
    2022-09-23 mmuetzel Dependencies- bugs #63093 is dependent
    2022-09-23 dasergatskov Attached File- Added fft2_octave72.png, #53745
    2022-09-23 None Attached File- Added octave.jpg, #53743
        Attached File- Added matlab.jpg, #53744

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