cross-spectral density matrix is rank deficient!

Michael Wibral wibral at BIC.UNI-FRANKFURT.DE
Fri May 16 10:35:02 CEST 2008


Hi Muthuraman,

could it be that you have removed some channels from your data and did not calculate a new headmodel/leadfield? As far as I remember this will cause a similar error message (although strictly speaking it shouldn't).

Michael


> -----Urspr√ľngliche Nachricht-----
> Von: FieldTrip discussion list <FIELDTRIP at NIC.SURFNET.NL>
> Gesendet: 15.05.08 20:51:27
> An: FIELDTRIP at NIC.SURFNET.NL
> Betreff: Re: [FIELDTRIP] cross-spectral density matrix is rank deficient!


> 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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> 
> 
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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.
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