[Mne_analysis] specify noise covariance rank in MNE-Python?

[Martin Luessi]

Hi,

The mne_inverse_operator command has an option to specify the rank of
the covariance matrix. This is useful when e.g. maxfilter has been
applied to the data and the rank has been reduced. It seems like this
option is currently missing from MNE-Python; we are computing an inverse
operator using a covariance matrix estimated from data with maxfilter
applied but the detected rank is 200  (only gradiometers) instead of 64.

Is there a reason for not having this option in MNE-Python or would it
make sense to add it?

Best,

Martin