Is there a way for breaking a loop iteration, if it takes to long?

Dear People, I am running analyzes of multiple input data files. Each file is analyzed in one iteration of a for loop, e.g.

for 1:length(data)
    analyze(data{i});
end

However, for some data, the analysis takes very long, because the RAM is full. Is there a way of breaking the loop on a timer or RAM condition, say after 1 hour of iteration time, or as RAM gets full? Or do you have any other recommendation, except for throughing the data away in advance, or tuning the analysis?

Kind regards, Philipp

Answer 1

[Jan Orwat]

One of the simplest ways for time control is to use tic and toc

time0 = tic;
timeLimit = 60*60*1; % 1 hour == 3600 seconds
  for ...
    ...
    if toc(time0)>timeLimit
      break
    end
  end

or using while loop

time0 = tic;
timeLimit = 60*60*1; % 1 hour == 3600 seconds
  while conds && toc(time0)<timeLimit
    ...
  end

in case of placing multiple breakpoints it is vital to identify them e.g. by printing breakpoint info. It is crucial to design breakpoints in a way allowing to resume computations from the point it was disrupted. Sometimes instead of command break it is better to put a message and a debbuger breakpoint which will give you command line access while program is paused. Then you can continue from this exact point in code.

[Philipp]

Dear Jan, thank you very much for this answer. However, I would be looking for a workaround that react on execution times of single functions without splitting the function up. In my example, the execution of analyze(data{i}) takes very long. Kind regards, Philipp

[Jan Orwat]

I thought it doesn't split the function. This wouldn't work for you?

t0 = toc;
tLimit = 3600;
for i = 1:length(data),
   analyze(data{i});
   if toc(t0)>tLimit, break; end
end

You can return later changing one line:

for i = whereIStopped:length(data)

Or do you want to stop the function "analyze" from further operation if it takes too long, and switch it off during operation?

[Jingying Wang]

I have the same Problem but I want to stop the function "analyze", or better to break the "for" circle. You know how?

[Gauri Kant]

This method still requires the function to terminate. I have a numerical optimisation function in the for loop that requires convergence. However, for one particular iteration, if there is no convergence within 5 mins, I wish to skip that iteration and move to the next. Any clue as to how that might be possible?

[Walter Roberson]

@Gauri Kant

Use the Parallel Computing Toolbox.

Use parfeval() to start the computation of an interation. This will return a "future", which is a reference to a process. Use wait() to wait for the "future" with a timeout. If the timeout is encounted, then cancel() the "future"

This is pretty much the only method that MATLAB provides to kill a computation without the cooperation of the computation.

[Gauri Kant]

@Walter Roberson Thanks! This actually helped me!

Answer 2

[Jos (10584)]

You can create a timer ;

th = timer('TimerFcn','keyboard') ;
th.StartDelay = 5 ;

start(th) ;
pause ; % will be stopped after 5 seconds.
stop(th) ;

[Gauri Kant]

But this does not allow to move to the next iteration, does it?

[Walter Roberson]

You can have the timer routine set a shared variable that is being tested by the loop to know to move on.