[Mne_analysis] TFCE parameters

[Eric Larson]

>
> Is there any motivation behind start>0 other than trying to reduce
> computation time?
>

Not as far as I know.


> Why are these the 2 parameters we have control for TFCE?  What's to be
> gained/lost?
>

Think of it as a way to approximate an integral where each function value
to put into the summation takes a long time to compute (the clustering
step). Ideally we would start at zero and go in infinitesimal steps to the
largest statistic value, but numerically that's infeasible and practically
it would take forever. So the idea is to compute as few as possible
(highest start and biggest step) without affecting the result. If using a
smaller start and/or step affects the output, then you should use the
smaller start and/or step because it should provide a better approximation
to the integral. Without looking back, I would assume a start of 2 was
suggested because it usually doesn't affect the result (at least in the
suggester's experience).

Eric
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