Matlab clears persistent and global variables in fmincon when activating UseParallel

Question

H R 2021-4-6

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/794082-matlab-clears-persistent-and-global-variables-in-fmincon-when-activating-useparallel

编辑： Matt J 2021-4-7

It seems matlab clears all global and persistent variables within the objective function when using "UseParallel" in fmincon. I am trying to track each function call within the objective function (this is because my objective function should generate a specific input file to be called by an exteranl program and give a misfit output).

I use the folowing code to within my objective function to generate the unique file name at each iteration:

persistent count_1
if isempty(count_1)
    count=0;
else
    t = getCurrentTask();
    worker_number = t.ID;
    c = worker_number * 10000 + count_1;
    count =c;
    
    count_1=count_1+1;
end
count_1=count_1+1;
filename = ['Run_' num2str(cout) '.dat'];

But strangly, the name would not change after the first function call. Have you encoutered this issue?

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Answer 1

Matt J 2021-4-6

2
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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/794082-matlab-clears-persistent-and-global-variables-in-fmincon-when-activating-useparallel#answer_668317

编辑：Matt J 2021-4-6

This happens because, in parallel computing, it isn't easily definable what it means for a variable to "persist". A peristent variable is normally one that retains its value from the previous function call. But when the objective function calls are all executing simultaneously (or at least non-sequentially), what does "previous" even mean?

With global variables, similar ambiguities arise. What if two parallel-occuring executions of the objective function assign different values to a global variable G that they share with the base workspace? Which of the conflicting values should reside in the base workspace version of G after the execution is complete?