Using broadcasting array variable values as indexes

Question

Farbod Tavakkoli Khomeini 2019-10-18

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/486044-using-broadcasting-array-variable-values-as-indexes

编辑： Walter Roberson 2019-10-18

I am using parallel tool for running my code. Actually there is no major error and the code runs but I have some minor error such as "The entire array or structure 'AccelerationY' is a broadcast variable. This might result in unnecessary communication overhead". I have the same error in my code in four different places which I have indicated below with # in bold.

My first question is how can I solve this problem in my code. Second, does it really hurt the runtime of the code?. Because my code has a very high runtime.

I appreciate your kind help in advance,

carnum = data{1,1};
AccelerationY = data{1,2};
coordinationx = data{1,3};
coordinationy = data{1,4};
velocity = data{1,5};
parfor j=1:car
        x{j}=[];
        y{j}=[];
        speed{j}=[];
        AccX{j}=[];
        AccY{j}=[];
        z_gyro{j}=[];
        f=find(carnum == j);
        
        for a=f
            x{j} = [x{j},coordinationx(a,1)];                                        %#here for coordinationx
            y{j} = [y{j},coordinationy(a,1)];                                        %#here for coordinationy
            AccY{j} = [AccY{j},AccelerationY(a,1)];                          %#here for AccelerationY
            rr= velocity(a,1)/3.6;                                                       %#here for Velocity
            speed{j} =[speed{j},rr];
        end
end

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Answer 1

Walter Roberson 2019-10-18

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/486044-using-broadcasting-array-variable-values-as-indexes#answer_396955

In that code you cannot eliminate the broadcast variables.

If the arrays are large then there could potentially be a fair overhead in copying them into each worker.

You can, however, rewrite the entire code without parfor, by using a series of accumarray() or splitapply() calls, or you could switch to table representation and use table operations.