[Eeglablist] ICA and covariance matrix for CSP

[Bethel Osuagwu]

Dear Arno,

Thank you for your suggestion, although I don't know why precision matters but converting the data matrix to double precision allows the removal of a few ICA components without the need to reduce the number of channels.
With Single precision, removing 'n' components "causes" the warning unless I remove 'n+1' channels. But with double precision, the warning only occurs if a significant number of components(~8) are removed without reducing the number of channels.


Thanks
Bethel 
________________________________________
From: Arnaud Delorme [arno at ucsd.edu]
Sent: 02 May 2013 05:30
To: Bethel Osuagwu
Cc:
Subject: Re: [Eeglablist] ICA and covariance matrix for CSP

Dear Bethel,

does the warning also show up when you convert you data matrix to double precision (double function of Matlab).
Best,

Arno

On 25 Apr 2013, at 06:30, Bethel Osuagwu wrote:

Thank you Makoto for your reply.
Reducing the number of channels stops the warning, but I did not check if the number of channels I eliminated equals the number of components removed. I will check if that is true although I think its true.
Also I have been told from FieldTrip that the problem can be solved by regularizing the (inverse)covariance matrix(adding some estimated noise to the diagonals) but am not sure exactly how much noise and the effect of adding this noise.
Thanks
Bethel
________________________________________
From: Makoto Miyakoshi [mmiyakoshi at ucsd.edu<mailto:mmiyakoshi at ucsd.edu>]
Sent: 24 April 2013 21:14
To: Bethel Osuagwu
Cc:
Subject: Re: [Eeglablist] ICA and covariance matrix for CSP

Dear Bethel,

Sounds like it is because of reduced rank. Please try that you also discard the same number of channels after IC rejection to see what happens.

Makoto


2013/4/23 Bethel Osuagwu <b.osuagwu.1 at research.gla.ac.uk<mailto:b.osuagwu.1 at research.gla.ac.uk><mailto:b.osuagwu.1 at research.gla.ac.uk>>
Hi Everyone,

I have noticed that after using ICA to remove artifact in my signal, I can no longer compute the covariance matrices needed for common spatial pattern without matlab giving me warning regarding the accuracy of the estimated matrix. Indeed the estimated matrix is not accurate. This does not happen if I use only a small subset of my channels after removing noise with ICA.  If I do not use ICA at all the warning disappears.

I want to ask if anybody knows why ICA causes this issue and how I can fix it?

Thanks a lot.
Bethel Osuagwu
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--
Makoto Miyakoshi
Swartz Center for Computational Neuroscience
Institute for Neural Computation, University of California San Diego
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