Progress monitor (progress bar) that works with parfor

Monitoring the progress of a long-running parfor loop is not straightforward because the workers cannot communicate. This function gets around that limitation by storing the progress in a text file.

Example usage:

N = 100;
parfor_progress(N); % Initialize
parfor i=1:N
pause(rand); % Replace with real code
parfor_progress; % Count
end
parfor_progress(0); % Clean up