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_vb_get_Ab.m
    path of file: ./repos/bspm/thirdparty/spm8
    
    the code of the file until where you have to start completion: function [voxel] = spm_vb_get_Ab (Y,slice)
% Get A and b quantities - average prediction errors from AR model
% FORMAT [voxel] = spm_vb_get_Ab (Y,slice)
% 
% Y         data
% slice     data structure
% 
% voxel(n).A  
% voxel(n).b
%
% The above quantities are estimated using pre-computed
% cross-covariance matrices
%___________________________________________________________________________
% Copyright (C) 2008 Wellcome Trust Centre for Neuroimaging

% Will Penny and Nelson Trujillo-Barreto
% $Id: spm_vb_get_Ab.m 1143 2008-02-07 19:33:33Z spm $

k=slice.k;
N=slice.N;
    
for n=1:N,
    % Equation 63 of paper VB1 but implemented 

    
function [voxel] = spm_vb_get_Ab (Y,slice)
% Get A and b quantities - average prediction errors from AR model
% FORMAT [voxel] = spm_vb_get_Ab (Y,slice)
% 
% Y         data
% slice     data structure
% 
% voxel(n).A  
% voxel(n).b
%
% The above quantities are estimated using pre-computed
% cross-covariance matrices
%___________________________________________________________________________
% Copyright (C) 2008 Wellcome Trust Centre for Neuroimaging

% Will Penny and Nelson Trujillo-Barreto
% $Id: spm_vb_get_Ab.m 1143 2008-02-07 19:33:33Z spm $

k=slice.k;
N=slice.N;
    
for n=1:N,
    % Equation 63 of paper VB1 but implemented 
    % efficiently using cross-covariance method described in paper VB3
    if isfield(slice.I,'A2_tilde')
        A2_tilde=slice.I.A2_tilde(:,:,n);
    else
        A2_tilde=reshape(slice.I.S*slice.a2{n}(:),k,k);
    end