It is a matrix with ROIs x EEG activity obtained through source modelling.

I know how to do source modelling at least with cortical activity. Assuming that, how do I export to matlab the matrix of all EEG activity. Not for one ROI or one epoch. If it's possible.

I have tried to export functional connectivity graph o matrix or the sLORETA or dSPM but I don't think it's the correct way to do so because I obtain a tensor whose indices include 2 numbers with a "1" in the middle A x 1 x B which means is not giving me the full tensor.

To be sure we are talking of the same thing, once the source modelling (estimation) is performed, there estimated sources are EEG activity anymore, but the estimated source activity. From your comment, I guess that you want to extract a time series of brain (source) activity per ROI (scout). If this is the case, these time series can be extracted with the process Extract > Extract scout time series

The problem is that (three) input files do not share the same number of components per vertex (1 for constrained and 3 for unconstrained), so it is not possible to use PCA to extract the scout time series as it requires the same number of components and vertices in all the input files.

The issue is I think by one side the 3 components of the scout time series an the interpretation of it and the other issue is that I don't know what to do to obtain 175 scouts time series which is the whole brain in fact. Because I have only used cerebellum for the scouts time series I have obtained and it only has 33 scouts.