[FieldTrip] Question connectivity analysis / ICA / MVAR

Narayan P Subramaniyam narayan.ps at tut.fi
Tue Apr 23 09:36:16 CEST 2013


Although I am not an expert in connectivity analysis, but from a 
mathematical point of view it looks like the case where at least one 
variable in covariance matrix is a exact linear combination of other and 
hence it is not positive definite.
This could be due to rejection of few components by ICA ? Other experts 
may shed more light...


On 22/04/2013 21:36, Martin Winkels wrote:
> Hello Guys,
>
> I am trying to perform connectivity analysis in sensor domain 
> (fieldtrip and matlab are up to date). Within doing that I am facing a 
> small problem in the ICA analysis in combination with a MVAR analysis. 
> If I execute the following code, I get an error message as follows:
>
>
> Error using chol
> Matrix must be positive definite.
>
> Error in armorf (line 40)
> ap(:,:,1) = inv((chol(ap(:,:,1)/Nr*(Nl-1)))');
>
> Error in ft_mvaranalysis (line 390)
>             [ar, tmpnoisecov] = armorf(dat, numel(rpt{rlop}), 
> size(tmpdata.trial{1},2), cfg.order);
>
> Error in mu_firstexample (line 90)
> mdata           = ft_mvaranalysis(cfg, data_ma_ica);
>
>
> Can anybody help me with that issue?
>
>
> % artifact correction: ica component analysis
>
> cfg             = [];
> cfg.method      = 'runica';
> cfg.runica.pca   = 40;
> comp            = ft_componentanalysis(cfg, data_ma);
>
> cfg             = [];
> cfg.layout      = 'CTF275.lay';
> cfg.viewmode    = 'component';
> ft_databrowser(cfg, comp)
>
> %% artifact correction: ica component rejection
>
> cfg             = [];
> cfg.component   = [4]; % to be removed component(s)
> data_ma_ica     = ft_rejectcomponent(cfg, comp, data_ma);
>
> %% compute MVAR, spectral transfer and granger
>
> % mvar
> cfg             = [];
> cfg.order       = 5;
> cfg.toolbox     = 'bsmart';
>
> mdata           = ft_mvaranalysis(cfg, data_ma_ica);
>
>
> Thank you,
>
> -- 
> Martin Winkels
>
> B.Sc. / Ingenieur in
> Medizininformatik und Biomedizintechnik
>
> University of M√ľnster
>
> phone: +49 177 6090603 <tel:%2B49%20177%206090603>
> mail: m_wink10 at uni-muenster.de <mailto:m_wink10 at uni-muenster.de>
>
>
>
>
> _______________________________________________
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> fieldtrip at donders.ru.nl
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-- 
With Best Regards,
Narayan P Subramaniyam, M.Sc.
Researcher/PhD student
Department of Electronics and Communications Engineering
Tampere University of Technology
Finn-Medi 1, 4th Floor, Room 203
Biokatu 6, FI-33520 Tampere, Finland

Tel: +358 (0)40 198 1951
E-mail: narayan.ps at tut.fi

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