cross-spectral density matrix is rank deficient!

[jan-mathijs schoffelen]

Hi Muthuraman,

You are warned for the rank-deficiency of the csd-matrix, because this  
could lead to numerical instabilities when inverting this matrix.  
However, since fieldtrip uses pinv instead of inv, this does not lead  
to crashing scripts.
On the other hand, the message basically is the consequence of the fact that:

-you used too few trials to simulate the csd (the total number of  
tapers applied should ideally be > the number of channels),
-you did not add enough sensor noise to your simulation. because you  
typically want to simulate fewer sources than sensors (which by  
definition makes the true source csd-matrix rank deficient) you really  
have to add sensor noise,
-or both.

Good luck

Jan-Mathijs

Quoting Muthuraman Muthuraman <muthuraman10 at HOTMAIL.COM>:

>
> Hello Fieldtrippers,
>
> I get the warning "cross-spectral density matrix is rank deficient"   
> when running the sourceanalysis_DICS on simulated data.
> Any hints due to which the warning comes will be very helpfull,   
> because the channel combination was selected for ''all" in the   
> frequency analysis.
>
>
> Thanking you
>
> With regards,
> M.Muthuraman.
>
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The aim of this list is to facilitate the discussion between users of the FieldTrip  toolbox, to share experiences and to discuss new ideas for MEG and EEG analysis. See also http://listserv.surfnet.nl/archives/fieldtrip.html and http://www.ru.nl/fcdonders/fieldtrip.