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_fs_fmri_csd.m
    path of file: ./repos/ExploreASL/External/SPMmodified
    
    the code of the file until where you have to start completion: function [y] = spm_fs_fmri_csd(y,M)
% spectral feature selection for a CSD DCM
% FORMAT [y] = spm_fs_fmri_csd(y,M)
% y      - CSD

    
function [y] = spm_fs_fmri_csd(y,M)
% spectral feature selection for a CSD DCM
% FORMAT [y] = spm_fs_fmri_csd(y,M)
% y      - CSD
% M      - model structure
%__________________________________________________________________________
%
% This simply log-transforms the (real) auto-spectra
%
% David O, Friston KJ (2003) A neural mass model for MEG/EEG: coupling and
% neuronal dynamics. NeuroImage 20: 1743-1755
%__________________________________________________________________________
% Copyright (C) 2008 Wellcome Trust Centre for Neuroimaging
 
% Karl Friston
% $Id: spm_fs_fmri_csd.m 6662 2016-01-08 15:20:02Z adeel $


% return (scaled) cross-spectra and covariance functions
%--------------------------------------------------------------------------
c  = spm_csd2ccf(y,M.Hz);
% y  = [y; c(1:8:end