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 or
 averaged TFRs.

 The configuration can contain
   cfg.method         = 'sum', 'svd', 'abssvd', or 'complex' (default = 'sum')
   cfg.updatesens     = 'no' or 'yes' (default = 'yes')
 and for timelocked input data (i.e. ERFs), the configuration can also contain
   cfg.demean         = 'yes' or 'no' (default = 'no')
   cfg.baselinewindow = [begin end]

 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.