How can I execute two functions with a time delay between the two calls?

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Waseem AL Aqqad 2021-6-8

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https://ww2.mathworks.cn/matlabcentral/answers/851200-how-can-i-execute-two-functions-with-a-time-delay-between-the-two-calls

编辑： Waseem AL Aqqad 2021-6-12

I have the following script:

[G_d,G_o, isolated,active,phi] = Single_CF_initial(G,50,1,0.2);
for tt = 2:25
    if isolated(tt-1)- isolated(tt)==0
        break
    end
    [G_d, isolated,Needremove] = Single_CF_Stages(G_d,phi,isolated,active);
    [G_r,isolated] = H(G_d, G_o,0.95,isolated);
    G_d = G_r;
        
end

I want to call the function "H" after some time of calling both functions "Single_CF_initial" and "Single_CF_Stages". Let us say after 15 seconds.

Is it possible to accomplish this in MATLAB?

Thanks!

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Answer 1

Adam Danz 2021-6-8

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If you want execution to stay "busy" during the 15 sec wait time, use a simple tic/toc evaluation. It's not clear which of the two functions are invoked second or if that's subject to change, but the second one should set the start time using ts=tic; and then enter a while-loop until toc(ts)>=15 after which the H function can be called (I'm hoping that's just a paceholder for the actual function name). Note that the wait period could be placed at the end of the second function or outside of the functions after the second one is called.

If you want Matlab's busy state to be 'ready' during the 15 sec wait time, a much more efficient method would be to use a timer. The timer can be created any time before the functions are called and will have a start delay of 15 sec. After the second function is called you can merely start the timer and it will execute its callback function after 15 sec. See Timer Callback Functions. See this answer for an example of using a timer that sets a variable value 3 minutes after an app is started.

If you get stuck, share your updated code and let us know where you are at and what the problem is.

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Adam Danz 2021-6-8

编辑：Adam Danz 2021-6-8

在 MATLAB Online 中打开

Notes on precision of timing methods

All of Matlab's timing methods face precision limts but some are more variable than others (see documentation). For example, the pause() function is susceptible to variations due to your OS and concurrent system activity (see documentation). I explain limitations to tic/toc and the timeit functions in this answer. If you choose to use tic/toc you can optimize the method by following the advice in this answer.

To demonstrate, below is comparison of 11 iterations of pause(1) compared to 11 iterations of a while-loop waiting for 1-sec using tic/toc. The first iteration was removed for each comparison and I subtracted 1-second to display the error of each funciton (along with some unavoidable overhead). Variation between iterations has many sources incuding the JIT compiler method used in Matlab. tic/toc has less error than pause for this duration. However, pause is easier to implement and its error is still reasonable for most usecases.

clear

drawnow; pause(.5)

tt = zeros(1,11);

for i = 1:11

t = tic();

pause(1)

tt(i) = toc(t);

end

drawnow; pause(.5)

tt2 = zeros(1,11);

for i = 1:11

t = tic();

while toc(t)<1

% do nothing

end

tt2(i) = toc(t);

end

drawnow; pause(.5)

stem(2:11, tt(2:end)-1, 'b','DisplayName','pause')

hold on

stem(2:11, tt2(2:end)-1, 'r', 'DisplayName','TicTocLoop')

legend

xlabel('Iteration')

ylabel('error (sec)')

Waseem AL Aqqad 2021-6-10

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Hi Adam,

I'm sorry for my late reply. I just needed some time to understand the timer object, and also to make sure that what I want to accomplish is something realistic. The two functions "Single_CF_initial" and "Single_CF_Stages" emulate the cascading failure of routers in a network, and then I plot the number of failed routers per unit of time as figure 1 'attached'. The function H (Healing) recovers the failed routers. One of the inputs of H depends on the output of first two functions. Figure 2 is what I got when I called H from out of the while loop. Figure 3 is what I got when I called H from inside the while loop.

When I used both pause and timer object I got exactly the same figures (2 and 3). Based on the hypothesis that I buit, I supposed that I will get something similar to figure 1 but the curve should maintain the steady state at a value much lower than 2000( maximum no. of routers).

This is what I did:

[G_dmg,G_orig, isolated,active,phi] = Single_CF_initial(G,3,0,0.2);
for tt = 2:30
    if isolated(tt-1)- isolated(tt)==0
        break
    end
    
    [G_dmg, isolated,Needremove] = Single_CF_Stages(G_dmg,phi,isolated,active);
    t =  timer('Name','t','ExecutionMode','singleShot', ...
        'ObjectVisibility','off','StartDelay',15);  
    t.TimerFcn = @(t,Healing)disp('Hello World!');
    
    [G_rec,isolated] = Healing(G_dmg, G_orig,.1,isolated);
    G_dmg = G_rec;
end
figure
plot(1:length(isolated(1:end)),isolated(1:end)); hold on
title('Cascading Failure - Small World (Nodes=5000)');
xlabel('Time')
ylabel('No. of Isolated Nodes Per Unit Of Time')

I downloaded your demo "timerDemo.mlapp" but unfortunately, it didn't load when I opened it. So, I feel that I didn't fully understand timer object. To be honest with you, I got lost when I read the documentations.

Thanks.

Adam Danz 2021-6-11

编辑：Adam Danz 2021-6-11

Let's check if I got this right.

It starts by you simulating a network attack.

The router failures propagate to other routers in a domino effect

You want the Healing function to start 15 seconds after the start of the attack. The 2nd and 3rd inputs are available from the beginning of the simulation but the 1st input is continually updated during the simulation.

A timer function is almost perfect to solve this except that you need to access the current value of G_dmg. If you're doing this in an app or GUI or any type of figure, that problem can be solved by declaring G_dmg as a property of the app/figure; is that the case (we're avoiding global variables)?

But perhaps a timer could be avoided and the could be ever simpler. What controls the propagation? Is it done in a loop? If so, it would be easy and efficient to use tic/toc to control when healing begins by iteratively checking the time within the loop (assuming the loop iterates quickly). Is that the case? If propagation is not done in a loop, could you describe how that works?

Waseem AL Aqqad 2021-6-11

编辑：Waseem AL Aqqad 2021-6-11

在 MATLAB Online 中打开

Correct.

I'm not using an app or GUI. So, after generating the network, the propagation starts by choosing a no. of routers randomly, say two, and remove all their links (Stage 0) and this is done in function Single_CF_initial. The output of this function is passed as an input argument to function Single_CF_Stages, this function is composed of exactly 12 lines where it just compares the current no. of links of all other routers to a breakdown threshold and remove links of the routers that met the condition (gt the threshold) and this is Stage 1. After that I use a while loop in a script file as I showed earlier in my first comment to this answer. Please be noticed that the output of second function is passed as an input to it when it is called in the while loop to perform several stages.

[G_dmg,G_orig, isolated,active,phi] = Single_CF_initial(G,3,1,0.2);
t = 2;
while isolated(t-1)- isolated(t)~=0
    [G_dmg, isolated,Needremove] = Single_CF_Stages(G_dmg,phi,isolated,active);
    %[G_rec] = Healing(G_dmg, G_orig,.1);
    %G_dmg = G_rec;
    t = t+1;
end

EDIT: In my first comment I used a for loop cause I was trying to avoid an infinit loop when I call the healing funtion but the above script is the original one.

Adam Danz 2021-6-12

High five 🖐🏼

Waseem AL Aqqad 2021-6-12

High five 🖐 You’re the best.

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Answer 2

Gatech AE 2021-6-8

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编辑：Gatech AE 2021-6-8

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If you use the "pause" function, you can specify a time in seconds as the input. It does require integers and uses decimals as fractional seconds.

[G_d,G_o, isolated,active,phi] = Single_CF_initial(G,50,1,0.2);
waitTime = 15;
for tt = 2:25
    if isolated(tt-1)- isolated(tt)==0
        break
    end
    [G_d, isolated,Needremove] = Single_CF_Stages(G_d,phi,isolated,active);
    pause(waitTime)
    [G_r,isolated] = H(G_d, G_o,0.95,isolated);
    G_d = G_r;
    
end

If you don't know how long you'll actually need to pause in advance, using "input" is another option that pauses execution until an input is provided.