Vectorizing nested for loop

I am struggling to accurately vectorize this nested loop. Right now, the loop takes 2-8 hours to run, so I would like to reduce that time if possible. Help appreciated.

%% Parameters
m=3; %AR model order
lambda=225;%lambda=10 for smoothing priors
nfft=656 ; %(nearest even number of volume)
fs=0.7143;%1/TR

%add leading 0 for subject names
subject = sprintf('%06d',subject);

%files
ASCII_File = fullfile(['path/',num2str(subject),'/path/',num2str(subject),'_task-rest_acq-AP_run-01_bold_']);
outdir = fullfile(['path/',num2str(subject),'/path/']);
%% preallocate 
totalData = zeros(5632,88,657);
power = zeros(329,88);

%% subject
tStart = tic;
disp(["Begining MATLAB Processing of subject: ", num2str(subject)])    
    
for v = 0:656 
    n=v+1;
    vname=num2str(v.','%05d');
    BOLDdatafile = [ASCII_File,vname];

    Ascii = importdata(BOLDdatafile);
    totalData(:,:,n)=Ascii(:,:);
              
end

disp('Starting XYZ transformations')
for z=1:64 % z dimension
    X = ['z: ',num2str(z)];
    disp(X)
    power=[];
    volume=[];
    
    for y=1:88 % y dimension
        X = ['y: ',num2str(y)];
        disp(X)
        row= y+(88*(z-1)); %actual row number in ascii file
        disp(row)
        volume(:,:) = totalData(row,:,:);

        for x=1:88 % x dimension
            X = ['x: ',num2str(x)];
            rawy = volume(x,:).';
            %('1. SMOOTHING PRIORS')
            T=length(rawy);
            I=speye(T);
            D2=spdiags(ones(T-2,1)*[1 -2 1],[0:2],T-2, T);
            z_stat=(I-inv(I+lambda^2*D2'*D2))*rawy;
            SPy=z_stat;
            [pxx,f] = pburg(SPy,m,nfft,fs);
            power(:,x)=pxx;

        end

        for n=0:328
            oname=num2str(n.','RS_%05d');
            outfile=[outdir,oname];
            vol=n+1;
            if z==1
                dlmwrite(outfile,power(vol,:),'-append','delimiter',' ');
            else
                if y==1
                    dlmwrite(outfile,power(vol,:),'-append','delimiter',' ','roffset',1);
                else
                    dlmwrite(outfile,power(vol,:),'-append','delimiter',' ');
                end
            end
        end
    end
end

tEnd = toc(tStart);
fprintf('FINSHED! Time to completion: %d minutes and %.2f seconds\n', floor(tEnd/60), rem(tEnd,60));

Answer 1

[Sulaymon Eshkabilov]

Most of your simulation time because of the data import from other data file sources importdata() and exporting the data to external data file via dlmwrite().

It does not seem to be possible to vectorize these data import and export as shown in your code.

Note that importdata() is slow. If feasible, substitute it with some other data import fcns, such as textscan(), fscanf().