Can anyone help with using MATLAB builtin fft() function to do a centered FFT/DFT, see Wikipedia – Discrete Fourier Transform, Generalised / Centered.
The background is that I'm doing FFTs and inverse FFTs between a physical coordinate space and k-space for modelling of dispersive waves. So there are two reasons for requiring the centered FFT:
i. both domains have negative coordinates, centered around the origin; and,
ii. the origin in k-space is often undefined and so I'd like to body-swerve that whole issue by using even-length vectors/arrays, so that the origin itself is not included.
So far, I can do the calculation correctly if I manually construct a DFT matrix and premultiply the vectors (it's ok but less than ideal due to the computational complexity). However, I cannot seem to get this right when using phase shifts with fft().
The shifts I derived are obviously wrong, producing nonsense. I also tried the code here: https://se.mathworks.com/matlabcentral/fileexchange/55929-centered-fourier-transforms The real component is off-by-one and the imaginary component is nonzero when it shouldn't be.
I'm using a Guassian and a characteristic function for test purposes. Attached should be some sample code.
Does anybody know how to do the phase shifts correctly so that it'll work with MATLAB's builtin fft()?
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