You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: spm_eeg_fix_ctf_headloc.m
    path of file: ./repos/spm12/toolbox/MEEGtools
    
    the code of the file until where you have to start completion: function D = spm_eeg_fix_ctf_headloc(S)
    
function [grad] = ctf2grad(hdr, dewar)

% CTF2GRAD converts a CTF header to a gradiometer structure that can be
% understood by FieldTrip and Robert Oostenveld's low-level forward and
% inverse routines. The fieldtrip/fileio read_header function can use three
% different implementations of the low-level code for CTF data. Each of
% these implementations is dealt with here.
%
% See also READ_HEADER, FIF2GRAD, BTI2GRAD, YOKOGAWA2GRAD

% undocumented option: it will return the gradiometer information in dewar
% coordinates if second argument is present and non-zero

% Copyright (C) 2004, Robert Oostenveld
%
% This file is part of FieldTrip, see http://www.ru.nl/neuroimaging/fieldtrip
% for the documentation and details.
%
%    FieldTrip is free software: you can redistribute it and/or modify
%    it under the terms of the GNU General Public License as published by
%    the Free Software Foundation, either version 3 of the License, or
%    (at your option) any later version.
%
%    FieldTrip is distributed in the hope that it will be useful,
%    but WITHOUT ANY WARRANTY; without even the implied warranty of
%    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
%    GNU General Public License for more details.
%
%    You should have received a copy of the GNU General Public License
%    along with FieldTrip. If not, see <http://www.gnu.org/licenses/>.

% My preferred ordering in the grad structure is:
%   1st 151 coils are bottom coils of MEG channels
%   2nd 151 are the top coils of MEG channels
%   following coils belong to reference channels

if nargin<2 || isempty(dewar)
    dewar = 0;
end