MATLAB: Arrays of reduction variables

parfor loopreduction variable

In parallel computing toolbox, I want to create an array of reduction variables. Is it possible?
m=3; n=5;
b=zeros(m,2);
parfor i=1:n
  a=[i i+1];
  for j=1:m
    b(j,:)=b(j,:)+j*a;
  end
end
I get this result Error: The variable b in a parfor cannot be classified. See Parallel for Loops in MATLAB, "Overview".
Is there a way to make this work?
Matt

Best Answer

In this case, parfor doesn't understand the fact that you're performing independent reductions on the rows of b. You can convince it by performing the update to the whole of b all at once, like so:
m=3; n=5;
b=zeros(m,2);
parfor i=1:n
  a=[i i+1];
  btmp = zeros(m,2);
  for j=1:m
    btmp(j,:) = j*a;
  end
  b = b + btmp;
end
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