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_DEM_M_set.m
    path of file: ./repos/spm12
    
    the code of the file until where you have to start completion: function [M] = spm_DEM_M_set(M)
% sets indices and performs checks on hierarchical models
% FORMAT [M] = spm_DEM_M_set(M)
%
% for each level (i); required fields
%
%   M(i).g  = y(t)  = g(x,v,P)    {inline function, string or m-file}
%   M(i).f  = dx/dt = f(x,v,P)    {inline function, string or m-file}
%
% and
%
%   M(i).m  = number of inputs v(i + 1);
%   M(i).n  = number of states x(i);
%   M(i).l  = number of output v(i);
%
% or
%
%   M(i).x  = hidden states;
%   M(i).v  = causal states;
%
% for each level (i); optional fields
%
%   M(i).pE = prior expectation of p model-parameters
%   M(i).pC = prior covariances of p model-parameters
%   M(i).hE = prior expectation of h log-precision (cause noise)
%   M(i).hC = prior covariances of h log-precision (cause noise)
%   M(i).gE = prior expectation of g log-precision (state noise)
%   M(i).gC = prior covariances of g log-precision (state noise)
%   M(i).xC = prior covariances of states
%   M(i).Q  = precision components (input noise)
%   M(i).R  = precision components (state noise)
%   M(i).V  = fixed precision (input noise)
%   M(i).W  = fixed precision (state noise)
%
%
% sets fields, checks internal consistency of model specification and sets
% estimation parameters.  If a single hyperparameter is supplied i.i.d
% components are assumed (i.e., Q = I, R = I)
%--------------------------------------------------------------------------
%
%   M(1).E.s;     = smoothness (s.d. in time bins)
%   M(1).E.d;     = embedding order q(v)  (i.e., number of derivatives)
%   M(1).E.n;     = embedding order q(x)
%
% If the highest level involves any dynamic or static transformation
% of its inputs a further level is added with flat priors
%__________________________________________________________________________
% Copyright (C) 2008 Wellcome Trust Centre for Neuroimaging

% Karl Friston
% $Id: spm_DEM_M_set.m 7322 2018-05-31 09:47:15Z karl $

    
function [M] = spm_DEM_M_set(M)
% sets indices and performs checks on hierarchical models
% FORMAT [M] = spm_DEM_M_set(M)
%
% for each level (i); required fields
%
%   M(i).g  = y(t)  = g(x,v,P)    {inline function, string or m-file}
%   M(i).f  = dx/dt = f(x,v,P)    {inline function, string or m-file}
%
% and
%
%   M(i).m  = number of inputs v(i + 1);
%   M(i).n  = number of states x(i);
%   M(i).l  = number of output v(i);
%
% or
%
%   M(i).x  = hidden states;
%   M(i).v  = causal states;
%
% for each level (i); optional fields
%
%   M(i).pE = prior expectation of p model-parameters
%   M(i).pC = prior covariances of p model-parameters
%   M(i).hE = prior expectation of h log-precision (cause noise)
%   M(i).hC = prior covariances of h log-precision (cause noise)
%   M(i).gE = prior expectation of g log-precision (state noise)
%   M(i).gC = prior covariances of g log-precision (state noise)
%   M(i).xC = prior covariances of states
%   M(i).Q  = precision components (input noise)
%   M(i).R  = precision components (state noise)
%   M(i).V  = fixed precision (input noise)
%   M(i).W  = fixed precision (state noise)
%
%
% sets fields, checks internal consistency of model specification and sets
% estimation parameters.  If a single hyperparameter is supplied i.i.d
% components are assumed (i.e., Q = I, R = I)
%--------------------------------------------------------------------------
%
%   M(1).E.s;     = smoothness (s.d. in time bins)
%   M(1).E.d;     = embedding order q(v)  (i.e., number of derivatives)
%   M(1).E.n;     = embedding order q(x)
%
% If the highest level involves any dynamic or static transformation
% of its inputs a further level is added with flat priors
%__________________________________________________________________________
% Copyright (C) 2008 Wellcome Trust Centre for Neuroimaging

% Karl Friston
% $Id: spm_DEM_M_set.m 7322 2018-05-31 09:47:15Z karl $

% order
%--------------------------------------------------------------------------
g      = length(M);
 
% set missing fields
%==========================================================================
 
% check for specification of hidden states
%--------------------------------------------------------------------------
if isfield(M,'f') && ~isfield(M,'n') && ~isfield(M,'x')
    msgbox('please specify hidden states or their number')
end