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_preproc_write.m
    path of file: ./repos/spm/toolbox/OldSeg
    
    the code of the file until where you have to start completion: function spm_preproc_write(p,opts)
% Write out VBM preprocessed data
% FORMAT spm_preproc_write(p,opts)
% p    - results from spm_prep2sn
% opts - writing options.  A struct containing these fields:
%        biascor - write bias corrected image
%        cleanup - level of brain segmentation cleanup
%        GM      - flags for which images should be written
%        WM      - similar to GM
%        CSF     - similar to GM

    
function spm_preproc_write(p,opts)
% Write out VBM preprocessed data
% FORMAT spm_preproc_write(p,opts)
% p    - results from spm_prep2sn
% opts - writing options.  A struct containing these fields:
%        biascor - write bias corrected image
%        cleanup - level of brain segmentation cleanup
%        GM      - flags for which images should be written
%        WM      - similar to GM
%        CSF     - similar to GM
%__________________________________________________________________________

% John Ashburner
% Copyright (C) 2005-2022 Wellcome Centre for Human Neuroimaging


if ischar(p), p = cellstr(p); end