Behavior of parfeval when its input arguments get updated?

Question

Thang Luong 2013-10-1

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/88850-behavior-of-parfeval-when-its-input-arguments-get-updated

回答： Edric Ellis 2013-11-14

Hi all,

I'd like to make sure the new function parfeval (<http://www.mathworks.com/help/distcomp/parfeval.html>) meets my need before subscribing to Matlab 2013b. My question is as follows (see the example code below).

Suppose I have a variable x which is an argument to the function used in parfeval (in my example, it is @magic). As I am collecting results and updating x, will I (a) get the same results (the update of x doesn't affect parfeval), and (b) potentially get different results due to the update of x ? I'd really like to have (b) instead of (a).

    p = gcp();
    % To request multiple evaluations, use a loop.
    x = 0
    for idx = 1:10
      f(idx) = parfeval(p,@magic,1,x); % Square size determined by idx
    end
    % Collect the results as they become available.
    for idx = 1:10
      % fetchNext blocks until next results are available.
      [completedIdx,value] = fetchNext(f);
      fprintf('Got result with index: %d.\n', completedIdx);
      x = x + completedIdx; 
    end

Thanks,

Regards, Thang

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Answer 1

Edric Ellis 2013-11-14

1
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/88850-behavior-of-parfeval-when-its-input-arguments-get-updated#answer_115187

The updates to 'x' will not be seen by the workers. When you call PARFEVAL, the input arguments and function are all packaged up together ready to be sent to a worker, and the value of 'x' is copied into that package. So, you'll get (a).