The variable in parfor cant classified

Question

freebil 2013-7-4

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关闭： MATLAB Answer Bot 2021-8-20

Hello.This is my code:

c_hat = zeros(n,1);
vc = zeros(m,n);
cv = zeros(m,n);
parfor j = 1:n
        checks = find(H(:,j));
        allIncoming = cv(checks,j);
        sumAllIncoming = sum(allIncoming) + LLRs(j);
        c_hat(j) = (1 - sign(sumAllIncoming))/2;
        toCheck = sumAllIncoming -  allIncoming;
        vc(checks,j) = toCheck;
end

It is not runing because "The variable vc in a parfor cannot be classified." Without parfor it is running fine. Is it possible to run it with parfor?

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Answer 1

Matt J 2013-7-4

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https://ww2.mathworks.cn/matlabcentral/answers/81079-the-variable-in-parfor-cant-classified#answer_90806

编辑：Matt J 2013-7-4

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There are rules about sliced variables and how you can index them in parfor loops. However, you can get around these rules by re-organizing vc and cv as cell arrays,

    c_hat = zeros(n,1);
    vc = num2cell(zeros(m,n),1);
    cv = vc;
    parfor j = 1:n
            checks = H(:,j)~=0;
            allIncoming = cv{j}(checks);
            sumAllIncoming = sum(allIncoming) + LLRs(j);
            c_hat(j) = (1 - sign(sumAllIncoming))/2;
            toCheck = sumAllIncoming -  allIncoming;
            vc{j}(checks) = toCheck;
    end
    vc=[vc{:}]; %convert back to normal array

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freebil 2013-7-4

编辑：freebil 2013-7-4

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Really thanks, but i missed to say tha this parfor is inside a bigger loop.Sorry about this.The full function is:

[m n] = size(H);
c_hat = zeros(n,1);
LLRs = 2*y/sigma_2;
vc = zeros(m,n);
cv = zeros(m,n);
for iters = 1:maxiter
      for j = 1:n
          checks = find(H(:,j));
          allIncoming = cv{j}(checks);
          sumAllIncoming = sum(allIncoming) + LLRs(j);
          c_hat(j) = (1 - sign(sumAllIncoming))/2;
          toCheck = sumAllIncoming -  allIncoming;
          vc{j}(checks) = toCheck;
      end
      if( sum(mod(H*c_hat,2)) == 0 )
          return;
      end
      for j = 1:m
          vars = find(H(j,:));
          allIncoming = tanh(vc(j,vars)/2);
          prodAllIncoming = prod(allIncoming);
          toVar = prodAllIncoming./allIncoming;
          cv(j,vars) = 2*atanh(toVar);
      end
end

I cannot parfor the iters because there is return inside this loop.So i have to parfor the insider loops..I would appreciate it if you help me more.After the changes i have the problem"Conversion to cell from double is not possible.

Conversion to cell from double is not possible.
Error in decodeBP (line 57)
        cv(j,vars) = 2*atanh(toVar);

freebil 2013-7-4

在 MATLAB Online 中打开

Really thanks for the answers. @Jan Simon line 35 was

vc{j}(checks) = toCheck;

and line 19 was

parfor j = 1:n

@Matt J I changed them but now i have the error

Index exceeds matrix dimensions.

Error in decodeBP (line 52)
        allIncoming = tanh(vc{j}(vars)/2);

Matt J 2013-7-4

编辑：Matt J 2013-7-4

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I take it back. Put this back

vc=[vc{:}];

but add immediately after it

vc=num2cell(vc,2);

Also, please learn to use DBSTOP to trap and investigate common errors like "Index exceeds matrix dimensions." and "Conversion to cell from double is not possible."