Storing a matrix in a file.

close all;

location = '/MATLAB Drive/PE/Frames/';       %  folder in which your images exists
ds = imageDatastore(location) ;              %  Creates a datastore for all images in your folder
i=1;
array=zeros(65,1080,1920);
while hasdata(ds) 
   Img = readimage(ds,i);
   %i=i+1;
   %Img = read(ds);             % read image from datastore
   %figure, imshow(img);    % creates a new window for each image

    
    %Img = imread('Circle.png'); % real miscroscope image of cells
    Img=double(Img(:,:,1));
    
    %% parameter setting
    timestep=25;  % time step
    mu=0.2/timestep;  % coefficient of the distance regularization term R(phi)
    iter_inner=5;
    iter_outer=40;
    lambda=5; % coefficient of the weighted length term L(phi)
    alfa=15;  % coefficient of the weighted area term A(phi)
    epsilon=150; % papramater that specifies the width of the DiracDelta function
    
    sigma=1.5;     % scale parameter in Gaussian kernel
    G=fspecial('gaussian',15,sigma);
    Img_smooth=conv2(Img,G,'same');  % smooth image by Gaussiin convolution
    [Ix,Iy]=gradient(Img_smooth);
    f=Ix.^2+Iy.^2;
    g=1./(1+f);  % edge indicator function.
    
    % initialize LSF as binary step function
    c0=2;
    initialLSF=c0*ones(size(Img));
    % generate the initial region R0 as a rectangle
    initialLSF(1:1080, 1:1920)=-c0;  
    phi=initialLSF;
    
    figure(1);
    mesh(-phi);   % for a better view, the LSF is displayed upside down
    hold on;  contour(phi, [0,0], 'r','LineWidth',2);
    title('Initial level set function');
    view([-80 35]);
    
    figure(2);
    imagesc(Img,[0, 255]); axis off; axis equal; colormap(gray); hold on;  contour(phi, [0,0], 'r');
    title('Initial zero level contour');
    pause(0.5);
    
    potential=2;  
    if potential ==1
    potentialFunction = 'single-well';  % use single well potential p1(s)=0.5*(s-1)^2, which is good for region-based model 
    elseif potential == 2
    potentialFunction = 'double-well';  % use double-well potential in Eq. (16), which is good for both edge and region based models
    else
    potentialFunction = 'double-well';  % default choice of potential function
    end
    
    
    % start level set evolution
    for n=1:iter_outer
    phi = drlse_edge(phi, g, lambda, mu, alfa, epsilon, timestep, iter_inner, potentialFunction);
    if mod(n,2)==0
        figure(2);
        imagesc(Img,[0, 255]); axis off; axis equal; colormap(gray); hold on;  contour(phi, [0,0], 'r');
    end
    end
    
    % refine the zero level contour by further level set evolution with alfa=0
    alfa=0;
    iter_refine = 10;
    phi = drlse_edge(phi, g, lambda, mu, alfa, epsilon, timestep, iter_inner, potentialFunction);
    
    finalLSF=phi;
    figure(2);
    imagesc(Img,[0, 255]); axis off; axis equal; colormap(gray); hold on;  contour(phi, [0,0], 'r');
    hold on;  contour(phi, [0,0], 'r');
    str=['Final zero level contour, ', num2str(iter_outer*iter_inner+iter_refine), ' iterations'];
    title(str);
    
    pause(1);
    figure;
    mesh(-finalLSF); % for a better view, the LSF is displayed upside down
    hold on;  contour(phi, [0,0], 'r','LineWidth',2);
    str=['Final level set function, ', num2str(iter_outer*iter_inner+iter_refine), ' iterations'];
    title(str);
    axis on;

    array(i)=finalLSF;
    i=i+1;

end

Gives Error:In contour (line 51)
In PE (line 47) 
Unable to perform assignment because the left and right sides have a different number of elements.

Error in PE (line 90)
    array(i)=finalLSF;

Answer 1

[dpb]

 array(i)=finalLSF;

tries to stuff the RHS into a single array location where finalLSF was defined as whatever the result of

     phi = drlse_edge(phi, g, lambda, mu, alfa, epsilon, timestep, iter_inner, potentialFunction);
    finalLSF=phi;

turns out to be. If, as the comments say, that's something that could be displayed meaningfully with countour, then it's obvious it can't be a single number.

It looks like you've lost track of what your variables mean at this point; use the debugger and set a breakpoint and your logic error will likely become obvious.