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: ft_preproc_smooth.m
    path of file: ./repos/spm/external/fieldtrip/preproc
    
    the code of the file until where you have to start completion: function [datsmooth] = ft_preproc_smooth(dat, n, tol)

% FT_PREPROC_SMOOTH performs boxcar smoothing with specified length.
% Edge behavior is improved by implicit padding with the mean over
% half the boxcar length at the edges of the data segment.
%
% Use as
%   [dat] = ft_preproc_smooth(dat, n)
%
% Where dat is an Nchan x Ntime data matrix, and n is the length
% of the boxcar smoothing kernel
%
% If the data contains NaNs, these are ignored for the computation, but
% retained in the output.
%
% See also PREPROC

% Undocumented options:
%  n can also be a vector containing a custom smoothing kernel
%  n can also be 'regsmooth', using a regularised estimate of the first temporal derivative 
%
% Copyright (C) 2010, Stefan Klanke
%
% This file is part of FieldTrip, see http://www.fieldtriptoolbox.org
% 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.
%

    
function [datsmooth] = ft_preproc_smooth(dat, n, tol)

% FT_PREPROC_SMOOTH performs boxcar smoothing with specified length.
% Edge behavior is improved by implicit padding with the mean over
% half the boxcar length at the edges of the data segment.
%
% Use as
%   [dat] = ft_preproc_smooth(dat, n)
%
% Where dat is an Nchan x Ntime data matrix, and n is the length
% of the boxcar smoothing kernel
%
% If the data contains NaNs, these are ignored for the computation, but
% retained in the output.
%
% See also PREPROC

% Undocumented options:
%  n can also be a vector containing a custom smoothing kernel
%  n can also be 'regsmooth', using a regularised estimate of the first temporal derivative 
%
% Copyright (C) 2010, Stefan Klanke
%
% This file is part of FieldTrip, see http://www.fieldtriptoolbox.org
% 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/>.
%
% $Id$

% preprocessing fails on channels that contain NaN
if any(isnan(dat(:)))
  ft_warning('FieldTrip:dataContainsNaN', 'data contains NaN values');
end