Problem with ifftn and ifftshift??

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Bran
Bran 2013-6-26
评论： Walter Roberson 2023-10-14
Hi there I was wondering if someone could help me. I am using the fftn fftshift functions as part of my alogrithm;
tmp = fftn(MAT); Adash = fftshift(tmp);
Adashup=ifftshift(Adash);
Adashup2new = ifftn(Adashup);
However, When I took everything else out and left these in as a tester I noticed that instead of the above taking me back to the original MAT, it alters the numbers quite a lot. What am I doing wrong?? Example original file MAT has a min of 0 and a max of 1.0856, however the file Adashup2new has a min of -6.792 and a max of 1.0856
  2 个评论
Mehri Mehrnia
Mehri Mehrnia 2023-10-14
why we should use fftshit?when I dont use fftshit, scale is good and untouched
Walter Roberson
Walter Roberson 2023-10-14
@Mehri Mehrnia
fft() returns back the 2-sided fft. By convention, the order of frequency bins returns back from fft() of real input signals is like
0, 1, 2, 3, 4, ... n-1, n, conj(-n), conj(-(n-1)), ... conj(-(4)), conj(-(3)), conj(-(2)), conj(-1)
but people often prefer to visualize it in the order
conj(-(n-1)), ... conj(-(4)), conj(-(3)), conj(-(2)), conj(-1), 0, 1, 2, 3, 4, ... n-1, n
The change is not mathematically significant: it is just easier for people to look at the plots.

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采纳的回答

Nitin
Nitin 2013-6-26
Sounds like Imaginary components are there due to round off errors, try extracting the real part
f = real(ifft2(F));

更多回答（1 个）

Bran
Bran 2013-6-27
Thanks so much for the help! I will try your suggestion! :D

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