The variable in parfor cant classified

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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

在 MATLAB Online 中打开

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."

The variable in parfor cant classified

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