How to run two loops simulatenously which share varaibles in MATLAB?

Question

Ryan 2022-12-22

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https://ww2.mathworks.cn/matlabcentral/answers/1883172-how-to-run-two-loops-simulatenously-which-share-varaibles-in-matlab

回答： Kunal Kandhari 2023-1-18

I am trying to implement some logic which can be simplified in the example below:

count = 5;
value = 0;
parfor i = 1:2
    if i == 1
        for u = 0:count
            %Do dome work
            pause(5);
            value = value + 1;
        end
    else
        while true
           disp(value)
           if(value > count)
               break
           end
           end
        end
    end
end

I wanted to run two loops in parallel which share a certain variable(s). Above is the closest I could get. I realized if I used the parfor as shown, I can call each on its own worker. Unfortunately, I am getting the error The PARFOR loop cannot run due to the way variable 'value' has been used

Anyone with an idea how I can achieve the above successfully?

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Answer 1

Kunal Kandhari 2023-1-18

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在 MATLAB Online 中打开

Hi,

Not all MATLAB for loops can be converted to parfor.

In your this part of code:

disp(value)
if(value > count)
   break
end

there is an dependency of variable value on the following piece of code:

value = value + 1;

This stops you from being able to use a parfor.

To solve these problems, you must modify the code to use parfor. The body of the parfor-loop is executed in a parallel pool using multiple MATLAB workers in a nondeterministic order. Therefore, you have to meet following requirements for the body of the parfor-loop:

The body of the parfor-loop must be independent. One loop iteration cannot depend on a previous iteration, because the iterations are executed in parallel in a nondeterministic order.

You can read more sbout the same using the following resources: