ifft2 with "symmetric option"
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Hi, I am looking at "ifft2" in matlab ( https://it.mathworks.com/help/matlab/ref/ifft2.html#bvjz37f-symflag ) and it introduces a "symmetric" option, that treats the matrix as a conjugate symmetric.
What does it mean " treats the matrix as a conjugate symmetric"?
If my matrix is not, what does it do?
Chunru on 23 May 2022
Edited: Chunru on 23 May 2022
Let F(u, v) be the forward FFT2 of f(x, y). For real function f(x,y), FT exhibits conjugate symmetry, i.e. F(u, v) = F*(-u, -v). Therefore if the input to IFFT2 is conjugate symmetric, the output will be the real. It is also possible to save some computations in this case comapreing general complex IFFT2.
In practical situation, the input to IFFT2(F), i.e. F, can be non-symetric conjugate even for real f due to rounding error. Therefore a flag 'symmetric' will treat input F as conjugate symmetric and allows faster IFFT2 and ensure the output to be real.