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: cat_vol_qa.m
    path of file: ./repos/ExploreASL/External/SPMmodified/toolbox/cat12
    
    the code of the file until where you have to start completion: function varargout = cat_vol_qa(action,varargin)
% CAT Preprocessing T1 Quality Control
% ______________________________________________________________________
% 
% Estimation of image quality measures like noise, inhomogeneity,
% contrast, resolution, etc. and scaling for school marks. 
%
% [QAS,QAM] = cat_vol_qa(action,varargin)
% 
%
% 1) Use GUI interface to choose segmentation and automatic setting of 
%    original and modified image (if available)
%     [QAS,QAM] = cat_vol_qa()                = cat_vol_qa('p0')
%
%     [QAS,QAM] = cat_vol_qa('p0'[,opt]) 
    
function     = which('cat_vol_qa');
      QAS.software.markdefs     = which('cat_stat_marks');
      QAS.software.qamethod     = action; 
      QAS.software.date         = datestr(clock,'yyyymmdd-HHMMSS');
      warning off
      QAS.software.opengl       = opengl('INFO');
      QAS.software.opengldata   = opengl('DATA');
      warning on
      QAS.software.cat_warnings = cat_warnings;
 
      %QAS.parameter             = opt.job; 
      if isfield(opt,'job')
        QAS.parameter.opts        = opt.job.opts;
        QAS.parameter.extopts     = opt.job.extopts;
        %QAS.parameter.output      = opt.job.output;
        if exist('res','var')
          rf = {'Affine','lkp','mn','vr'}; % important SPM preprocessing variables
          for rfi=1:numel(rf)
            if isfield(res,rf{rfi}), QAS.parameter.spm.(rf{rfi}) = res.(rf{rfi}); end