[FieldTrip] bemcp vs dipoli

[Maris Skujevskis]

Hi Fieldtrip users,

When constructing a volume conduction model for EEG using the boundary
element method (BEM), there are two methods available: 'dipoli' and
'bemcp'. Besides technicalities (i.e., 'dipoli' only available on Linux),
are there any differences that you know of/have experienced that make one
method better (more reliable, more accurate, or anything else that makes
you prefer one rather) than the other?

For some of my EEG subjects, 'dipoli' succeeds where 'bemcp' fails. During
processing with 'bemcp' there is a "warning: Matrix is singular, close to
singular or badly scaled. Results may be inaccurate. RCOND = NaN", with the
end result being that vol.mat contains NaNs.
The input in both cases, besides the method chosen, is identical.

Taking one step back in the processing pipeline, I am aware that a poor
segmentation outcome might be a/the cause of the warnings and eventual
errors when constructing a volume conduction model. But in general this
should hold equally for both methods. What I am wondering about is why one
method might deal more successfully than the other with the same input.

Best,
Maris
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