Clean the super-subject matrix of the vertices that have 0 value or are not
located on the cortex, according to FreeSurfer *cortical.mask.mgh file
distributed in inst/extdata. This function is used in
build_supersubject.
Clean the super-subject matrix of the vertices that have 0 value or are not
located on the cortex, according to FreeSurfer *cortical.mask.mgh file
distributed in inst/extdata. This function is used in
build_supersubject.