Question

I have a matlab script which executes 5 algorithm sequentially. All these 5 algorithms needs to run for 10 different initialization.

Whenever there is an error in i-th initialization, the script exit with an error message. I fix the issue(say, data issue) and start running the script again which executes from the first initialization.

I dont want to my code to run for previously executed initialization. ( from 1 run to i-1 the run)

One way is to reassign the value of index to start from i, which in turn require to modify the scrip everytime again and again.

Is there any way to restart the script from the i-th initialization onwards which dont require to modify the script?

Answer 1

Another technique you might like to consider is checkpointing. I’ve used something similar with long-running (more than one day) loops operating in an environment where the machine could become unavailable at any time, e.g. distributed clusters of spare machines in a lab.

Basically, you check to see if a ‘checkpoint’ file exists before you start your loop. If it does than that suggests the loop did not finish successfully last time. It contains information on where the loop got up to as well as any other state that you need to get going again.

Here’s a simplified example:

function myFunction()

  numIter = 10;
  startIter = 1;

  checkpointFilename = 'checkpoint.mat';

  % Check for presence of checkpoint file suggesting the last run did not
  % complete
  if exist(checkpointFilename, 'file')
    s = load(checkpointFilename);
    startIter = s.i;
    fprintf('Restarting from iteration %d\n', startIter);
  end

  for i = startIter:numIter
    fprintf('Starting iteration %d\n', i);
    expensiveComputation();
    save(checkpointFilename, 'i');
  end

  % We succefully finished. Let's delete our checkpoint file
  delete(checkpointFilename);

  function expensiveComputation()
    % Pretend to do lots of work!
    pause(1);
  end

end

Running and breaking out with ctrl-c part way through looks like this:

>> myFunction
Starting iteration 1
Starting iteration 2
Starting iteration 3
Starting iteration 4
Operation terminated by user during myFunction/expensiveComputation (line 27)

In myFunction (line 18)
    expensiveComputation();

>> myFunction
Restarting from iteration 4
Starting iteration 4
Starting iteration 5
...