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: file_exist.m
    path of file: ./repos/fieldtrip/external/brainstorm/private
    
    the code of the file until where you have to start completion: function isExist = file_exist(filename)
% FILE_EXIST: Test the existence of an absolute file path on the disk.
%             Replacement for the Matlab call "exist(..., 'file')" that gives unexpected results
%             when the file is somewhere in the Matlab path.

% @=============================================================================
% This function is part of the Brainstorm software:
% https://neuroimage.usc.edu/brainstorm
% 
% Copyright (c)2000-2020 University of Southern California & McGill University
% This software is distributed under the terms of the GNU General Public License
% as published by the Free Software Foundation. Further details on the GPLv3
% license can be found at http://www.gnu.org/copyleft/gpl.html.
% 
% FOR RESEARCH PURPOSES ONLY. THE SOFTWARE IS PROVIDED "AS IS," AND THE
% UNIVERSITY OF SOUTHERN CALIFORNIA AND ITS COLLABORATORS DO NOT MAKE ANY
% WARRANTY, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO WARRANTIES OF

    
function isExist = file_exist(filename)
% FILE_EXIST: Test the existence of an absolute file path on the disk.
%             Replacement for the Matlab call "exist(..., 'file')" that gives unexpected results
%             when the file is somewhere in the Matlab path.

% @=============================================================================
% This function is part of the Brainstorm software:
% https://neuroimage.usc.edu/brainstorm
% 
% Copyright (c)2000-2020 University of Southern California & McGill University
% This software is distributed under the terms of the GNU General Public License
% as published by the Free Software Foundation. Further details on the GPLv3
% license can be found at http://www.gnu.org/copyleft/gpl.html.
% 
% FOR RESEARCH PURPOSES ONLY. THE SOFTWARE IS PROVIDED "AS IS," AND THE
% UNIVERSITY OF SOUTHERN CALIFORNIA AND ITS COLLABORATORS DO NOT MAKE ANY
% WARRANTY, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO WARRANTIES OF
% MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE, NOR DO THEY ASSUME ANY
% LIABILITY OR RESPONSIBILITY FOR THE USE OF THIS SOFTWARE.
%
% For more information type "brainstorm license" at command prompt.
% =============================================================================@
%
% Author: Francois Tadel, 2011-2013

% Empty variable
if isempty(filename)
    isExist = 0;
% File is a root folder: let's consider it exists
% elseif strcmp(filename, bst_fileparts(filename))
elseif isequal(filename, '/') || isequal(filename, '\')
    isExist = 1;
% File does not exist: no ambiguity
elseif isempty(dir(filename))
    isExist = 0;
% File exists: we have to make sure it is NOT relatively to the current path
else
    % Check the file relative to the current Matlab folder
    pwdPath = pwd;
    pwdFile = [pwdPath '/' filename];
    % If it does NOT exist: no ambiguity, file exists
    if isempty(dir(pwdFile))
        isExist = 1;
    % Else: we consider that the file exists only in the current folder is a root folder
    % (=> folder = folder's parent)
    elseif strcmp(pwdPath, bst_fileparts(pwdPath, 1))
        isExist = 1;
    else
        isExist = 0;
    end