problem with using parfor

Hello All,

I am trying to make use of parfor, but I keep getting the following error "parfor cannot run due to the way the variable 'data' is used." Any thoughts?

Thanks in advance

    parfor iel=1:tne
        start=(iel-1)*576+1;
        end1=576*iel;
        data(start:end1)=data2(iel,:);
    end

Answer 1

[Walter Roberson]

    parfor iel=1:tne
        data((iel-1)*576+1:576*iel)=data2(iel,:);
    end

That is, MATLAB can analyze literal indices in ways that it cannot do when those indices are computed.

However, unless you have good reason not to, you should simply create data as a 576 x something array and without using parfor,

    data(:, 1:tne) = data2(:, 1:tne) .';
    

... especially if you can manage to compact it down to just

    data = data2 .';

After the copying has been done with 2D indices, then it is very fast to

    data = reshape(data, 1, []);

[Diab Abueidda]

Many thanks Walter for the answers!

I could not follow what you have mentioned. May you elaborate more?

Thanks

[Walter Roberson]

What is size(data) before the parfor loop? What is size(data2) ? What is tne ?

[Diab Abueidda]

Before the parfor loop data is initialized as

data=zeros(tne*576,1);

tne is the total number of elements in the finite element analysis. What I am trying to do is construct the global stiffness matrix as a sparse matrix.

parfor iel=1:tne
        data((iel-1)*576+1:576*iel)=data2(iel,:);
end
K=sparse(row,col,data,ndof,ndof)

size of data2 is tnex576

[Walter Roberson]

Then

data = reshape(data2.', 1, []);

with no loop.

[Diab Abueidda]

Oops! You are right!

Thanks a lot