[FieldTrip] code change in ft_compute_leadfield.m

[Johanna Zumer]

Dear FieldTrip users,

I've made a small change to ft_compute_leadfield (available in tonight's
release) regarding how the 'reducerank' option is handled, if multiple
dipole locations are entered all at once into ft_compute_leadfield.m.

This will *not* affect the vast majority of users, since usually
ft_compute_leadfield is called by higher FT functions and not directly by
users.

For example, it will not affect you if you create a leadfield either by
calling ft_prepare_leadfield or by letting ft_sourceanalysis compute the
leadfield for you (regardless of your 'reducedrank' option), since these
higher level FT functions call ft_compute_leadfield in a for-loop over
dipole location (and _not_ multiple dipole locations at once).

For completeness, here's a list of (rare) cases when it will affect your
results:

1) If you call ft_compute_leadfield directly with Nx3 dipoles (N>1) and
reducerank='yes' (or =2)

2) If you use a refdip in beamformer_DICS or beamformer_PCC, or a supdip in
beamformer_PCC, of *more than 1 dipole location* at a time (Nx3 refdip or
subdip, where N>1), AND you specified reducerank='yes' (or =2) in any of
these cases.

3) Default behaviour of calling ft_dipolefitting will not change.   However
if you call dipole_fit directly with more than one dipole AND
reducerank='yes' (or =2).

Please let me know if this isn't clear.

Best,
Johanna
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