error using parfor loop - Dimensions of arrays being concatenated are not consistent

I got the parallel toolbox to help me with this part of my code (takes weeks to compute). I am not sure where and how best to use the parfor..

I get errors like "Dimensions of arrays being concatenated are not consistent" when i implement it as below

 KD=WQ';
   hh=[];
   HH=[]; 
  gf=size(KD,2);
  FF=length(Ped);toc;
  %%
  for l=1:FF 
  for i =1:gf
   YY{i}=KD{l,i};
   r=size(YY{i},1);
% U=zeros(1,length(Arc));
parfor kk=1:r
    u=length(YY{i}(kk,:));
    uu=YY{i}(kk,:);
    Find1=[uu(1:u-1);uu(2:u)];Find1=Find1';
    [C,ia,ib] = intersect(Arc,Find1,'rows');
    U(ia)=1;
    
    HH=[HH;U];
     hh=[hh;length(Find1)-1];
    U=zeros(1,length(Arc));
   
end

  end
  end

Answer 1

[Lokesh]

Hello red,

In a 'parfor' loop, temporary variables are cleared at the beginning of each iteration.

In your code, the variable 'U' is cleared at the start of each iteration, leading to issues. To resolve this, ensure that 'U' is initialized before it is used.

Refer to the following code for guidance:

parfor kk = 1:r
    u = length(YY{i}(kk, :));
    uu = YY{i}(kk, :);
    Find1 = [uu(1:u-1); uu(2:u)];
    Find1 = Find1';
    [C, ia, ib] = intersect(Arc, Find1, 'rows');
    U = zeros(1, length(Arc)); % Initialize U here
    U(ia) = 1;
    
    HH = [HH; U];
    hh = [hh; length(Find1) - 1];
end

For more information, please refer to the documentation on Temporary variables in 'parfor':

https://www.mathworks.com/help/parallel-computing/temporary-variable.html

[Walter Roberson]

Also, I would recommend

    uu = YY{i}(kk, :);
    Find1 = [uu(1:end-1); uu(2:end)].';
    [C, ia, ib] = intersect(Arc, Find1, 'rows');
    U = zeros(1, length(Arc)); % Initialize U here
    U(ia) = 1;
    
    HH = [HH; U];
    hh = [hh; size(Find1,2)];

I have to wonder whether Find1 is being constructed properly; it is currently being constructed as a single row.