Trouble getting data outside of parfor loop

Hello, I have a process that needs to be applied to a 90 trials of an 11 electrode signal. The result of each trial is in the form of 11 different matrices of a number of rows that varies between trials (no greater than 12). I'm having trouble getting those matrices stored without matlab saying it can't be done whilst using parfor.

I create giant matrices of zeros outside the loop that has enough space for the max possible number of rows. Then inside the loop I try and pass the data to giantmatrix(rowNumber:rowNumber + row length of data, :).

clear all
matlabpool;
load MIdata25;
fs = 160;
numberElectrodes = 11;

Left1 = zeros(15*length(squeeze(thinkLeft(1, :, 1))), 1312);
Left2 = zeros(15*length(squeeze(thinkLeft(1, :, 1))), 1312);
Left3 = zeros(15*length(squeeze(thinkLeft(1, :, 1))), 1312);
Left4 = zeros(15*length(squeeze(thinkLeft(1, :, 1))), 1312);
Left5 = zeros(15*length(squeeze(thinkLeft(1, :, 1))), 1312);
Left6 = zeros(15*length(squeeze(thinkLeft(1, :, 1))), 1312);
Left7 = zeros(15*length(squeeze(thinkLeft(1, :, 1))), 1312);
Left8 = zeros(15*length(squeeze(thinkLeft(1, :, 1))), 1312);
Left9 = zeros(15*length(squeeze(thinkLeft(1, :, 1))), 1312);
Left10 = zeros(15*length(squeeze(thinkLeft(1, :, 1))), 1312);
Left11 = zeros(15*length(squeeze(thinkLeft(1, :, 1))), 1312);

parfor currentTrial = 1:length(squeeze(thinkLeft(1, :, 1)))
    currentTrial
    chanNum = 0;
    signalL=[];
    signalTotal=[];
    for currentElectrode = [2 6 8 9 11 13 14 16 20 41 42]
       %matrix indexing stuff
        signalTotal = [signalTotal; signalL3'];
    end
    x = %process applied to signalTotal

      for currentElectrode = 1:11
          xxl = zeros(numberElectrodes, length(signalL(1, :)));
          for imfNo = 1:length(squeeze(x(1, :, 1)))
            %matrix re-indexing stuff
          end
          if currentElectrode == 1
              Left1(((currentTrial-1)*15)+1:((currentTrial-1)*15)+length(xxl(:, 1)), :) = xxl;
          elseif currentElectrode == 2
              Left2(((currentTrial-1)*15)+1:((currentTrial-1)*15)+length(xxl(:, 1)), :) = xxl;
          elseif currentElectrode == 3
              Left3(((currentTrial-1)*15)+1:((currentTrial-1)*15)+length(xxl(:, 1)), :) = xxl;
          elseif currentElectrode == 4
              Left4(((currentTrial-1)*15)+1:((currentTrial-1)*15)+length(xxl(:, 1)), :) = xxl;
          elseif currentElectrode == 5
              Left5(((currentTrial-1)*15)+1:((currentTrial-1)*15)+length(xxl(:, 1)), :) = xxl;
          elseif currentElectrode == 6
              Left6(((currentTrial-1)*15)+1:((currentTrial-1)*15)+length(xxl(:, 1)), :) = xxl;
          elseif currentElectrode == 7
              Left7(((currentTrial-1)*15)+1:((currentTrial-1)*15)+length(xxl(:, 1)), :) = xxl;
          elseif currentElectrode == 8
              Left8(((currentTrial-1)*15)+1:((currentTrial-1)*15)+length(xxl(:, 1)), :) = xxl;
          elseif currentElectrode == 9
              Left9(((currentTrial-1)*15)+1:((currentTrial-1)*15)+length(xxl(:, 1)), :) = xxl;
          elseif currentElectrode == 10
              Left10(((currentTrial-1)*15)+1:((currentTrial-1)*15)+length(xxl(:, 1)), :) = xxl;
          elseif currentElectrode == 11
              Left11(((currentTrial-1)*15)+1:((currentTrial-1)*15)+length(xxl(:, 1)), :) = xxl;
          end
      end
      midpointL(currentTrial, :) = length(xxl(:, 1));
  end

With matlab showing problems with Left1-9, though it seems fine with midpointL.

[Walter Roberson]

Try replacing the length(xx1(:,1)) with numberElectrodes since you built xx1 with numberElectrodes as the first dimension.

Answer 1

[John Doe]

The answer to this was that matlab does not like "parfor variable +/- integer" as it thinks it'll be used to reference a previous loop which it can't do in parallel. In this case it's the variable CurrentTrial. Creating a 3d matrix instead of a 2d one with CurrentTrial used to define the first column solved it.

Answer 2

[Matt J]

I create giant matrices of zeros outside the loop that has enough space for the max possible number of rows. Then inside the loop I try and pass the data to giantmatrix.

A better idea would probably be to dispense with Left1...9 and instead store the results (of different sizes) in a 90x11 cell array. Then combine them after the loops end as needed.

 N=length(squeeze(thinkLeft(1, :, 1)));

 LoopData=cell(N, 11);

   parfor currentTrial = 1:N

      for currentElectrode = 1:11

          xxl = ...;

          LoopData{currentTrial,currentElectrode}=xxl;

      end

end

Now you can combine all the different xxl in LoopData using cell2mat() or similar...