Note that this reference documentation is identical to the help that is displayed in MATLAB when you type “help ft_combineplanar”.

  FT_COMBINEPLANAR computes the planar gradient magnitude over both directions
  combining the two gradients at each sensor to a single positive-valued number. This
  can be done for single-trial/averaged planar gradient ERFs or single-trial/averaged
  Use as
    [data] = ft_combineplanar(cfg, data)
  where data contains an averaged planar gradient ERF or single-trial/averaged TFR.
  The configuration can contain
    cfg.method         = 'sum', 'svd', 'abssvd', or 'complex' (default = 'sum')
  In the case of ERFs, the configuration can contain
    cfg.demean         = 'yes' or 'no' (default = 'no')
    cfg.baselinewindow = [begin end]
  After combining the planar data, the planar gradiometer definition does not
  match the data any more and therefore it is removed from the data. With
    cfg.combinegrad  = 'yes'
  the function will try to reconstruct the axial gradiometer definition.
  To facilitate data-handling and distributed computing you can use
    cfg.inputfile   =  ...
    cfg.outputfile  =  ...
  If you specify one of these (or both) the input data will be read from a *.mat
  file on disk and/or the output data will be written to a *.mat file. These mat
  files should contain only a single variable, corresponding with the
  input/output structure.