Unsure why parfor loop does not work in this case

Hello,

I am in the process of converting my initial multilogic module (Multilogic_v4.m) into a parallel version (MultiLogic_v1_parallel.m). I use two functions: my own MAPR function and I use the permn function. I am mostly done but I cannot get the last line of code in the main module to work and I am not sure why. My guess is that parfors may have some kind of limitation with concatenating strings?

I would appreciate if anyone can take a look at my code and tell me what I seem to be doing wrong.

FYI - I disabled the "while" loop in the parallel version for debugging.

Thanks to the community!

Dave

Answer 1

[Walter Roberson]

N_New{h+1} = N{h+1}+1;

That is one update of N_New

N_New{h+1} = numel(SSet);

and that is a second update within the same parfor.

%while N_New{h+1} > N{h+1} && N_New{h+1} < MValU ^ (MValU ^ Arity)

Do not use N_New that way. Use a temporary variable and store the final results into N_New before the end of the parfor

Answer 2

[Edric Ellis]

The problematic variables appear to be both M and P. For M, you have multiple different "reads" from the variable after the initial assignment. Perhaps try

  mVal = MAPR(MValU, Arity, OValU);
  M{h+1} = mVal;
  ...
    S{h+1} = mVal(:,j)'; % etc.

Likewise with P

  pVal = permn(SSet,Arity);
  P{h+1} = pVal;
  ...
       V{h+1}{a,1} = dec2base(pVal(j,a),MValU,size(M{h+1},1));

[dsmalenb]

Edric,

Thank you for your insights. I think it partially solved the issue. Unfortunately, the same line (Line 63) still errors out but now for a different reason.

Error using MultiLogic_v2_parallel>(parfor supply)
Reference to a cleared variable V.
Error in MultiLogic_v2_parallel (line 13)
parfor h=0:MValU^(MValU^Arity)-1 

If I comment out line 63 then it runs and all variable, including V are not empty. I am certainly confused now.

[Edric Ellis]

Ah, with that updated code, you have a problem with V because there are two different indexing forms. You probably need the same trick again

vVal = dec2base(..);
V{h+1}{a,1} = vVal;
...
    Q{h+1} = strcat(Q{h+1},vVal(k));

[dsmalenb]

Do you mean like so (see bwlow). It is running now but it is not producing the correct output.

for j=1:size(P{h+1},1)
    for a=1:Arity
        vVal = dec2base(pVal(j,a),MValU,size(M{h+1},1));
        V{h+1}{a,1} = vVal;
        %V{h+1}{a,1} = dec2base(pVal(j,a),MValU,size(M{h+1},1));
    end
    
    
    Z{h+1} = '';
    for k=1:size(M{h+1},1)
        Q{h+1} = '';
        for a=1:Arity
            Q{h+1} = strcat(Q{h+1},vVal(k));
            %Q{h+1} = strcat(Q{h+1},V{h+1}{a,1}(k));  % Does not like this one line
        end
        loc{h+1} = base2dec(Q{h+1},MValU) + 1;
        Z{h+1} = strcat(Z{h+1},num2str(M{h+1}(loc{h+1},Arity+1)));
    end
    Z{h+1} = base2dec(Z{h+1},MValU);
    SSet = [SSet, Z{h+1}];
    SSet = unique(SSet);
    N_New{h+1} = numel(SSet);
end