parfor in matlab. sliced variable and nested loop

问题:

I did my best to follow the documentation of the parallel toolbox, but still I could not avoid the problem of reusing array that was indexed in a nested loop. The problem is with variable node

parfor i=1:nX
   for j=1:nY


    [ind,dist]=findInCircle(node(i,j,:), part,r);

    UV=calcVelocity(part(ind,:), dist,node(i,j,:)) ;


    %here matlab complains that node is not indexed properly
    node(i,j,3)= UV(1);
    node(i,j,4)= UV(2);
    node(i,j,5)= UV(3);



   end


end

I do not use the array outside of the nested loop, the indexing is also according to the rule. Did I miss another parfor restriction?

回答1:

According to the documentation you can not use different indices like you did:

Within the first-level parenthesis or braces, the list of indices is the same for all occurrences of a given variable.

A simple workaround is possible:

parfor i=1:nX
   nodeSlice=node(i,:,:)

   for j=1:nY


    [ind,dist]=findInCircle(nodeSlice(j,:), part,r);

    UV=calcVelocity(part(ind,:), dist,nodeSlice(j,:)) ;


    %here matlab complains that node is not indexed properly
    nodeSlice(j,3)= UV(1);
    nodeSlice(j,4)= UV(2);
    nodeSlice(j,5)= UV(3);



   end
   node(i,:,:)=nodeSlice;

end

Get a slice from the matrix which contains all indices, work with it and then return it.