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_online_filter_init.m
    path of file: ./repos/spm12/external/fieldtrip/preproc
    
    the code of the file until where you have to start completion: function FM = ft_preproc_online_filter_init(B, A, x)

% function FM = ft_preproc_online_filter_init(B, A, x)
%
% Initialize an IIR filter model with coefficients B and A, as used in filter and butter etc.
% One sample x of the signal must be given as a column vector.
%
% This function will calculate the filter delay states such that the initial response
% is as if 'x' would have been applied since forever.
%
% See also FT_PREPROC_ONLINE_FILTER_APPLY

% 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/>.
%
% $Id$


    
function FM = ft_preproc_online_filter_init(B, A, x)

% function FM = ft_preproc_online_filter_init(B, A, x)
%
% Initialize an IIR filter model with coefficients B and A, as used in filter and butter etc.
% One sample x of the signal must be given as a column vector.
%
% This function will calculate the filter delay states such that the initial response
% is as if 'x' would have been applied since forever.
%
% See also FT_PREPROC_ONLINE_FILTER_APPLY

% 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/>.
%
% $Id$

% Normalize filter coefficients if not already done so
A = A(:); % use column vector
B = B(:); % use column vector

if A(1)~=1
  B = B/A(1);
  A = A/A(1);
end