The variable 'counter' is perhaps intended as a reduction variable, but is actually an uninitialized temporary.

Question

zein 2022-4-8

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1691520-the-variable-counter-is-perhaps-intended-as-a-reduction-variable-but-is-actually-an-uninitialized

回答： Rik 2022-4-8

I have tried to use parfor to decrease the required time needed for the for loop. The normal for loop was working properly before using parfor but it takes too long to finish the for loop. Then, I have modified the for to parfor to enable using parallel computing. The following error was generated (Error: The variable 'counter' is perhaps intended as a reduction variable, but is actually an uninitialized temporary).

start=8;%%%% elemnent that are not numbers in the file read
var=['_var_',num2str(no_variables),'_'];
a=first;
b=last;
tic
name=first;
counter=0;
for i=a:step:b
    filename=[surfacename,num2str(sub),var,num2str(i),'.raw'];
    fullname=fullfile(Dir,filename);
    fid = fopen(fullname,'rb'); % rb = read binary
    NN=N*10;
    data2 = fread(fid,NN,'single');
    fclose(fid);
    start=8;
    data2=data2(start:length(data2));
    len=length(data2)/no_variables;
    counter=counter+1;
    if opt==1 ||opt==6;
    data(:,counter)=data2(1:len);
    elseif opt==2;
    data(:,counter)=data2(len+1:2*len);
    elseif opt==3;
    data(:,counter)=data2(2*len+1:3*len);
    elseif opt==4;
    data(:,counter)=data2(3*len+1:4*len);
    elseif opt==5;
    data(:,counter)=data2(4*len+1:5*len);
    elseif opt==7;
    F = scatteredInterpolant(x,y,z,data2(1:len),'linear','linear');
    data_int=F(xq,yq,zq);
    data_int_2= reshape(data_int,[],1);
    data(:,counter)=data_int_2;
    end
      if mod(i,500) == 0
      fprintf('flie read %d...\n',i);
      tt=toc/60
      end
      name=[name,i];
end
tt=toc/60

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Answer 1

Rik 2022-4-8

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1691520-the-variable-counter-is-perhaps-intended-as-a-reduction-variable-but-is-actually-an-uninitialized#answer_937740

Your loop depends on the previous iterations. You should calculate the value of the counter variable inside the loop. Otherwise you cannot make this parallel.