I am getting different values of fft for the same variable as demonstrated by a simple example below...

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Yogesh
Yogesh 2024-5-9
回答： Paul 2024-5-11
Ran in:
E=[1 2 4 6;3 6 3 9;7 5 8 9]
E = 3x4
1 2 4 6 3 6 3 9 7 5 8 9
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EF=fftshift(abs(fft(E)))
EF = 3x4
4.5826 3.0000 5.2915 3.6056 15.0000 24.0000 11.0000 13.0000 4.5826 3.0000 5.2915 3.6056
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ES=fftshift(abs(fft(E(:,1))))
ES = 3x1
5.2915 11.0000 5.2915
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shouldn't ES be equal to the first row of EF...

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回答（1 个）

Paul
Paul 2024-5-11
Ran in:
I think you were expecting ES be equal to the first column of EF.
If desired for fftshift to work along a specific dimension of the input, then that dimension needs to be specified
E=[1 2 4 6;3 6 3 9;7 5 8 9];
EF=fftshift(abs(fft(E)),1) % specify the dimension
EF = 3x4
5.2915 3.6056 4.5826 3.0000 11.0000 13.0000 15.0000 24.0000 5.2915 3.6056 4.5826 3.0000
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ES=fftshift(abs(fft(E(:,1))))
ES = 3x1
5.2915 11.0000 5.2915
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If that second argument to fftshift is not specified, then the the 2D input is assumed to be a 2D fft, as might be produced from fft2, and the shifting is done in both dimensions.

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