Unclassified variables in a parfor loop

I am trying to do something like the following:

parfor i= xystart:xyend
    ....
    xycount = i - xystart + 1;
    A = zeros(nx,ny); B = A;
    
    for n=1:Nn;
        for m=1:Mm;
            A(m,n)= <some expression>;
            B(m,n)= <some expression>;
        end
    end
    C(xycount,:,:) = A. * B;
    
end 

I am getting an error message saying that 'C' is an unclassified variable. The above snippet is not the actual code which is quite big. But I hope the lines above convey what am I trying to do. Any idea what am I doing wrong?

Thanks!

[Mohammad Sami]

Try initializing variable C before calling the parfor loop.

Answer 1

[Matt J]

parfor i= 1:xyend-xystart+1
    ....
   
    A = zeros(nx,ny); B = A;
    
    for n=1:Nn;
        for m=1:Mm;
            A(m,n)= <some expression>;
            B(m,n)= <some expression>;
        end
    end
    C(i,:,:) = A. * B;
    
end 

[oceanmod]

Thanks! Is there a reason why changing the loop index like this fixes the problem?

[Matt J]

It satisfies restrictions on sliced variables listed here

https://www.mathworks.com/help/parallel-computing/sliced-variable.html#bq_ysmm-1