Nested for loop - adding elements to a matrix

Hello MathWorks community,

The below code is supposed to take in 6 by X by Y multidimensional array, run some calculations and give me three outputs as shown below in the methods diagram (first diagram). Measurement A = SS_Dur and measurement B = SS_Fre.

The trouble that I am having right now is regarding the nested for loop.

Each time the nested for loop is completed it generates 6 (number of channels) by 1 column. I need the for loop to keep adding this 6 x 1 column result to a bigger matrix so that if you input 6 files (or 6 epochs in this example) it will return 6 X 6 matrix.

However I am completely stuck on how best to do this. The attempt that I am showing down below is to first generate a matrix of zeros ("EEG_NofSC = zeros (Nchannels,Nepochs);") so that the nested floor loop can add its calculations into the zeros matrix.

However whenever I try this the resulting matrix is always the result from the LAST epoch only. I then checked the outputs within the Matlab command window and realised that the code that I have is actually overwriting the results (second digram).

So my question now here is how would I amend the code below so that the nested for loop properly add the outputs of its calculations into the "EEG_NofSC = zeros (Nchannels,Nepochs)" giving me a 6 by X number of epochs matrix? (hope the diagrams and the code makes sense!)

%% ===== RUN =====
function OutputFiles = Run(sProcess, sInputs) %#ok<DEFNU>

    % Initialize returned list of files
    OutputFiles = {};
    Nepochs = length(sInputs); % Numer of inputs or epochs
    EpochN = linspace (1,(Nepochs),(Nepochs)); % Changes the x-axis from time (s) to epoch number n. 
    FreqS  = 1024; % Sampling Frequency
    DataMat = in_bst(sInputs(1).FileName, [], 0);
    epochSize = size(DataMat.F);    
    Nchannels = epochSize(1); % Number of ALL channels (i.e. EEG, EOG, EMG and status)

    SS_Dur = zeros (Nchannels,Nepochs); % Creates Nchannels X Nepochs matrix of zeros
    SS_Fre = zeros (Nchannels,Nepochs); % Creates Nchannels X Nepochs matrix of zeros

    % ===== LOAD THE DATA =====   
    for iNepochs = 1 : Nepochs
       DataMat = in_bst(sInputs(iNepochs).FileName, [], 0);
       epochSize = size(DataMat.F);  
       Ntime = epochSize(2); % Number of time samples 
       Data = DataMat.F; 

          Data_Pos = Data>0;
          Channel   = zeros (1,Ntime);
          EEG_NofSC = zeros (Nchannels,Nepochs);
          %for j = 1 : Nepochs

            for i = 1 : Nchannels
                Channel(1,:)   = Data_Pos(i,:);
                SChanges       = xor(Channel(1:end-1),Channel(2:end));
                % Count the number of incidences where a sign change occurs
                EEG_NofSC(i,:) = sum(SChanges); % Number of sign changes
            end

       NofZ = sum(Data==0,2);

    SS_Dur(:,iNepochs) = (Ntime-1)/FreqS;
    SS_Fre = 1./(SS_Dur./Count0);
    end

Unrecognized function or variable 'Nepochs'.

Answer 1

[Bruno Luong]

Try this modification

EEG_NofSC = zeros (Nchannels,Nepochs); % move outside the outer loop
for iNepochs = 1 : Nepochs
    ...
    for i = 1 : Nchannels
        ...
        EEG_NofSC(i,iNepochs) = sum(SChanges); % assign to the single element not the whole row
    end
   ...
end

It seems you need to work to improve your programming skill.

[MinChul Park]

Thank you for your answer!