How to stop an iteration inside a for loop when its execution exceeds some period of time

Hello,

I have the following problem. I'm iterativing in a for loop. Sometimes an iteration takes a lot of time, therefore I want to skip it and move to the next iteration. I tried with tic toc but it does not seem to work.

Here is the code :

for i=1:9

       [alpha_w2u,C_w2u,m_w2u] = FL_WSGP1(xu,yu,d,eps1,sigma,K,c,b,0.5 *10^(i-5)) ;
       pFeLi.f = @(xk) pred1(alpha_w2u,C_w2u,m_w2u,xk,K,0) ;
       ctrl = @(t,xu) ctrlFeLi(t,xu,pFeLi,reffun);
       
       tic
       while (toc<2)
          [t4u,x4u] = ode45 (@(t4u,x4u) dynAffine(t4u,x4u,ctrl,pdyn),[0 50],xin);
       end
       x4uop(i) = x4u(end) ;
       
end      

How can I stop the execution of :

[t4u,x4u] = = ode45 (@(t4u,x4u) dynAffine(t4u,x4u,ctrl,pdyn),[0 50],xin);

if it takes more than 2 seconds and then move to the next iteration.

Thanks in advance

Answer 1

[Walter Roberson]

use an ode event function

@(t,y)my_event(t,y,tic)

have the function test whether toc() of the input tic exceeds the limit and if so signal termination

[Khalil Messaoudi]

Hello,

The idea looks good but it's still abstract how to implement the function, can you give more details please ?

Thanks in advance

[Khalil Messaoudi]

I created this function but I get the error message 'too many output arguments'

options = odeset('Events',@(t,y) interrupt(t,y,tic)) ;
          [t4u,x4u] = ode45 (@(t4u,x4u) dynAffine(t4u,x4u,ctrl,pdyn),[0 50],xin,options);






function [isterminal] = interrupt(t,y,inittime)
inittime = tic ;
if toc(inittime) < 2
    isterminal = 0 ;
else
    isterminal = 1 ;
end

Please tell if you see the location of the error in the interrupt function

[Walter Roberson]

https://www.mathworks.com/help/matlab/math/ode-event-location.html#bu7wfry

You need to define 3 outputs

[Walter Roberson]

inittime = tic ;

remove that line

[Khalil Messaoudi]

From what I understand from the documentation, 'isterminal' is what stops the execution of ode45 and that's all what I need. I don't understand the necessity of adding the two other outputs 'value' and 'direction' or what value should I assign to them.

[Torsten]

function [value,isterminal,direction] = interrupt(t,y,inittime)
  value = toc(inittime) - 2.0;
  isterminal = 1;
  direction = 0;
end

[Khalil Messaoudi]

@Torsten After multiple executions, I found out that a problem is still there.

In your suggestion, toc(inittime) actually calculates how long an ODE45's single step size lasts, not how long the whole process of ODE45 lasts, that I actually need. Therefore, if ODE45 takes a lot of time because the step sizes are very small, the function 'interrupt' does not solve my problem.

Do you have an idea on how to solve this ? thanks in advance

[Torsten]

Take inittime as

inittime = tic

before you call ode45.

Pass "inittime" to "interrupt". Taking "toc(inittime)" therein gives you the elapsed time since you called ode45.

So ode45 will stop if the elapsed time since you called it is > 2 seconds.

Or do I miss something ?

[Khalil Messaoudi]

@Torsten now it seems to work thnak you !

Answer 2

[Image Analyst]

I don't think you can programmatically stop a canned function once it's been called. But for other situations...

Try this:

for k = 1 : 100000
    startTime = tic; % Time at start of this iteration.
    % some code that takes time...then, whenever you want to check on the time:
    elapsedSeconds = toc(startTime);
    if elapsedSeconds > 2
        continue;
    end
end