clean up the code for Granger computation

[schoffelen]

In order to be able to do a meaningful and somewhat computationally constrained GC computation the code that is currently in place needs to be cleaned up a bit, in order to use:

• the new vismot_spectral functionality
• parcel-based GC computation, with the possibility to constrain the labels
• optional spatial prewhitening of the data before source reconstruction etc.

[schoffelen]

• the new vismot_spectral functionality (done)
• parcel-based GC computation, with the possibility to constrain the labels (done)
• optional spatial prewhitening of the data before source reconstruction etc. (done)

Test running at the moment, to check whether everything runs through.

@matsvanes this is an update

[schoffelen]

GC results have been computed. In trying to write the output as cifti files, for easier exploration of the results in HCP-workbench, I don't manage to do so anymore. I don't understand why, because I think that in the past this worked. @matsvanes this is an update.

[schoffelen]

For now I will put the granger stuff on hold. I have looked quite extensively at the results, and I think that the data is of insufficient quality to get stable enough estimates for meaningful comparison and statistics (mainly due to the limited number of trials per condition). The code has been pushed to the github repo. @matsvanes