[Mne_analysis] Source localization then Fourier transform vs the other way round

Gladia Hotan gladiach at gmail.com
Fri Jul 13 12:29:37 EDT 2018
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I'm thinking about frequency-domain source space results, specifically
whether doing source localization in the time domain then transforming to
the frequency domain is the same as transforming to the frequency domain
and then doing source localization. I found this archive post which states
that the FFT and other filtering procedures are right matrix
multiplications: https://mail.nmr.mgh.harvard.edu/pipermail/
/mne_analysis/2009-December/000336.html. This suggests that it doesn't
matter whether you localize first or Fourier transform first.

However, other sources say that Fourier transforms and filters are
typically implemented as matrices which are multiplied on the left of the
original signal. For example, this source multiplies the DFT matrix on the
left: https://ccrma.stanford.edu/~jos/st/Matrix_Formulation_DFT.html. This
source multiplies filter matrices on the left: https://www.dsprelated.

I'd have thought that if the inverse operator W is multiplied on the left
of the source activity x, then the filter/FFT matrix should also be
multiplied on the left; if the filter/FFT is applied on the right, I'd
expect that we'd have to modify W so that it is also multiplied on the

Could somebody shed some light on this?

Thanks and Best Regards,
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