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_init_block.m
    path of file: ./repos/bspm/thirdparty/spm8
    
    the code of the file until where you have to start completion: function [block] = spm_vb_init_block (Y,block)
% Initialise Variational Bayes for GLM-AR models
% FORMAT [block] = spm_vb_init_block (Y,block)
%
% Y             [T x N] time series with T time points, N voxels
% block         GLM-AR data structure
%
%___________________________________________________________________________
% Copyright (C) 2008 Wellcome Trust Centre for Neuroimaging


    
function [block] = spm_vb_init_block (Y,block)
% Initialise Variational Bayes for GLM-AR models
% FORMAT [block] = spm_vb_init_block (Y,block)
%
% Y             [T x N] time series with T time points, N voxels
% block         GLM-AR data structure
%
%___________________________________________________________________________
% Copyright (C) 2008 Wellcome Trust Centre for Neuroimaging

% Will Penny and Nelson Trujillo-Barreto
% $Id: spm_vb_init_block.m 2928 2009-03-24 08:54:32Z lee $

k=block.k;
p=block.p;
N=block.N;
T=block.T;
X=block.X;

%% Default optimisation parameters
if ~isfield(block,'tol')
    block.tol=0.0001;
end