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_dcm_virtual_electrodes.m
    path of file: ./repos/spm/toolbox/dcm_meeg
    
    the code of the file until where you have to start completion: function CSD = spm_dcm_virtual_electrodes(DCM,s,p,TYPE)
% Posterior estimates of coupling among selected populations
% FORMAT CSD = spm_dcm_virtual_electrodes(DCM,s,p,TYPE)
%
% DCM  -  inverted DCM (see below)
% s    -  indices of source, node or region
% p    -  indices of population in node
% TYPE -  {'CSD','CCF','DTF','GCA','COH','FSD'}
%
% If called  with an output argument, graphics will be suppressed
%
% Example:
% >> spm_dcm_virtual_electrodes(DCM,[1,2,1],[1,1,8],'DTF')
%

    
function CSD = spm_dcm_virtual_electrodes(DCM,s,p,TYPE)
% Posterior estimates of coupling among selected populations
% FORMAT CSD = spm_dcm_virtual_electrodes(DCM,s,p,TYPE)
%
% DCM  -  inverted DCM (see below)
% s    -  indices of source, node or region
% p    -  indices of population in node
% TYPE -  {'CSD','CCF','DTF','GCA','COH','FSD'}
%
% If called  with an output argument, graphics will be suppressed
%
% Example:
% >> spm_dcm_virtual_electrodes(DCM,[1,2,1],[1,1,8],'DTF')
%
% Estimates:
%--------------------------------------------------------------------------
% DCM.dtf                   - directed transfer functions (source space)
% DCM.ccf                   - cross covariance functions (source space)
% DCM.coh                   - cross coherence functions (source space)
% DCM.fsd                   - specific delay functions (source space)
% DCM.pst                   - peristimulus time
% DCM.Hz                    - frequency
%
% DCM.Ep                    - conditional expectation
% DCM.Cp                    - conditional covariance
% DCM.Pp                    - conditional probability
% DCM.Hc                    - conditional responses (y), channel space
% DCM.Rc                    - conditional residuals (y), channel space
% DCM.Hs                    - conditional responses (y), source space
% DCM.Ce                    - ReML error covariance
% DCM.F                     - Laplace log evidence
% DCM.ID                    - data ID
%__________________________________________________________________________

% Karl Friston
% Copyright (C) 2005-2022 Wellcome Centre for Human Neuroimaging

% population specific cross spectra
%--------------------------------------------------------------------------
M     = rmfield(DCM.M,'U');
ns    = length(DCM.Sname);        % number of sources
ne    = length(s);                % number of electrodes
qp    = DCM.Ep;                   % conditional expectations
qp.b  = zeros(2,ne) - 32;         % suppress non-specific and
qp.c  = zeros(2,ne) - 32;         % specific channel noise
M.l   = ne;

% defaults
%--------------------------------------------------------------------------
if nargin < 4, TYPE = 'CSD';             end