parfor循环不适用于MATLAB中的IF语句 [英] parfor loop won't work with IF statement in MATLAB

问题描述

parfor EEG_temp=10:100;
    EEG_temp_filter=filter(ones(1,EEG_temp),1,EEG_amp_vals(eeg_temp_subset,:),[],2);
    EEG_vertices=eeg_temp_subset((max(EEG_temp_filter,[],2)==EEG_temp)>0);
    connected_EEG_vertices=EEG_vertices((sum(surface.VertConn(EEG_vertices,EEG_vertices))>=2)>0);

    if length(connected_EEG_vertices)<5000 && length(connected_EEG_vertices)>500
        for fMRI_index=1:length(fMRI_thresholds);

            signal_union=union(connected_EEG_vertices,unique(fMRI_Vertices(fMRI_index,:)));
            signal_intersection=intersect(connected_EEG_vertices,unique(fMRI_Vertices(fMRI_index,:)));

            Overlap=length(signal_intersection)/length(signal_union)*100;
            highest_overlap=max(highest_overlap,Overlap)-Overlap;

            if highest_overlap==0;
                EEG_amp_value=[EEG_amp_value,EEG_amp];
                EEG_temp_value=[EEG_temp_value,EEG_temp];
                fMRI_amp_value=[fMRI_amp_value,fMRI_thresholds(fMRI_index)/100];
                highest_overlap=max(highest_overlap,Overlap);

            end

        end
    end % end of if
    % eeg_temp_subset=EEG_vertices;
end %end of EEG_temp

此代码试图最大化三个变量EEG_temp，EEG_amp和fMRI_amp，以确定哪种组合产生最高的重叠.因为我有一个可以为任务分配16个核心的集群，所以我认为parfor可以帮助加快分析速度，因为只有十个甚至数十万个组合.

This code is trying to maximize three variables, EEG_temp, EEG_amp, and fMRI_amp to determine which combination produces the highest overlap. Since there is 10s if not hundreds of thousands of combinations I thought parfor would help in speeding the analysis, since I have a cluster that can devote 16 cores to the task.

我遇到的问题是highest_overlap变量.如果我在parfor循环外定义它，MATLAB甚至不会让我开始运行分析，因为它是在parfor循环外定义的，但是，如果我不在parfor循环外定义它，则MATLAB崩溃时会崩溃. parfor循环，因为未定义.

The problem I am having is with the highest_overlap variable. If I define it outside of the parfor loop, MATLAB won't even let me start running the analysis because it is defined outside the parfor loop, however, if I don't define it outside the parfor loop MATLAB crashes when it gets to the parfor loop because it isn't defined.

任何人都可以提出建议来解决我遇到的问题吗?我认为IF语句可能与它有关，我必须按区别方式定义highest_overlap，因为如果我只是highest_overlap==overlap的话，它就告诉我我误用了highest_overlap多变的.因此，我将采用任何解决方案来使您可以使用此代码.只要是使用它，就可以改变使用最高重叠率的方式，也可以改变整个代码结构.

Can anyone offer a suggestion to fix the problem I have? I think the IF statement may have something to do with it, I had to define the highest_overlap the way it is where it is a differential because if I just did if highest_overlap==overlap, it told me I was misusing the highest_overlap variable. So I will take any solutions to get this code to work that you may have. Whether it is a change to the way highest overlap is used or to the entire code structure so long as it runs.

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Check out MATLAB's classification of parfor variables. Parfor is dumb and will scream if it's not clear what type of variable each one is.

在您的情况下，当在循环外未定义maximum_overlap时，它是一个临时变量，因此不会为循环的每次迭代保存，这对您的问题不起作用.鉴于MATLAB的逻辑，它必须是一个临时变量，因为您为其分配了变量，即

In your case, when highest_overlap is not defined outside of the loop, it's a temporary variable and thus not saved for every iteration of the loop which won't work for your problem. Given MATLAB's logic, it must be a temporary variable because you assign to it, that is

highest_overlap=max(highest_overlap,Overlap)-Overlap;

表示maximum_overlap是一个临时变量.然后，在parfor循环之外定义它时，它会看到临时变量已定义，并且会引发错误.

means highest_overlap is a temporary variable. When you then define it outside of the parfor loop, it sees that the temporary variable is already defined and will throw an error.

那么您如何解决呢?最简单的解决方案是使用切片变量.您可以预先分配一个向量，并将Overlap的值保存到该向量，然后进行缩减以实际解决parfor循环之外的maximum_overlap(不是差分).由于大部分计算时间可能花费在其他函数调用上，因此这仍然可以提供良好的加速效果.我不完全明白为什么在那里需要if语句，但是要使用切片变量(如我提到的那样)，您需要保存所有EEG_amp_value等内容以对变量进行切片，以恢复解决方案.

So how do you get around it? The easiest solution is to use sliced variables. You can preallocate a vector and save the values of Overlap to the vector and then do the reduction to actually solve for highest_overlap (not as a differential) outside of the parfor loop. Since most of the computing time is probably spent on the other function calls, this should still give a good speedup. I don't exactly see why you need that if statement in there but to use the slice variables as I mentioned you would need to save out all of the EEG_amp_value etc. to slice variables as well to recover the solution.

由于MATLAB parfor的工作方式，许多解决方案需要做一些事，这些事需要更多的内存来换取加速.我建议的方式将是这样.但是，如果您真的很小心，则可以将maximum_overlap归类为归约变量，然后它会起作用，但是我认为，因为它在if语句中，所以不可能.

Because of the way MATLAB's parfor works, many solutions require doing something that requires more memory using in return for the speedup. The way I suggested will be like that. However, if you are really careful, you may be able to get highest_overlap classified as a reduction variable and then it would work, but I think because it's in the if statement it cannot be.

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