Note that this reference documentation is identical to the help that is displayed in MATLAB when you type “help ft_source2full”.

  FT_SOURCE2FULL recreates the grid locations outside the brain in the source 
  reconstruction, so that the source volume again describes the full grid.
  This undoes the memory savings that can be achieved using FT_SOURCE2SPARSE
  and makes it possible again to plot  the source volume and save it to an
  external file.
  Use as
    [source] = ft_source2full(source)