You can use:

A = nan(m,n,...);

to initialize a matrix with NaN's, if that is what you ask for. Other popular choices are inf(m,n,...) to initialize with Inf's and ones(m,n,...) to initialize with 1's.

So, to create a 720x400 matrix full of NaN's you can just:

A = nan(720,400);

array2table works just fine. This takes a matrix and converts it to the table structure where each column of the matrix is a column in the output table:

>> N = NaN(10, 5);
>> T = array2table(N)

T = 

    N1     N2     N3     N4     N5 
    ___    ___    ___    ___    ___

    NaN    NaN    NaN    NaN    NaN
    NaN    NaN    NaN    NaN    NaN
    NaN    NaN    NaN    NaN    NaN
    NaN    NaN    NaN    NaN    NaN
    NaN    NaN    NaN    NaN    NaN
    NaN    NaN    NaN    NaN    NaN
    NaN    NaN    NaN    NaN    NaN
    NaN    NaN    NaN    NaN    NaN
    NaN    NaN    NaN    NaN    NaN
    NaN    NaN    NaN    NaN    NaN

Create a matrix of NaNs , use third output of the unique function to convert floating numbers to integer indexes and use matrix indexing to fill the matrices:

[t,~,it] = unique([t_A t_B]);
[L,~,iL] = unique([L_A L_B]);

A_new = NaN(numel(t),numel(L));
A_new(it(1:numel(t_A)),iL(1:numel(L_A))) = A;


B_new = NaN(numel(t),numel(L));
B_new(it(numel(t_A)+1:end),iL(numel(L_A)+1:end)) = B;

>> B1 = tb1; >> B1(A1==0) = NaN;

If I understand correctly what you want to do, this works: Img = uint8(randi([0 255], 5, 7)); % Create ‘Image’ [R,C] = size(Img); % Get ‘Image’ Dimensions nan_border = nan(R+2,C+2); % Create NaN Matrix nan_border(2:R+1, 2:C+1) = Img; % Insert ‘Image’ Into NaN Matrix nan_border = NaN NaN NaN NaN NaN NaN NaN NaN NaN NaN 60 23 185 253 185 201 28 NaN NaN 245 65 58 23 142 81 69 NaN NaN 158 219 147 82 135 115 134 NaN NaN 153 233 207 130 212 192 248 NaN NaN 44 179 103 15 219 28 181 NaN NaN NaN NaN NaN NaN NaN NaN NaN NaN

Try to use isnan for that.

TF = isnan(A) returns an array the same size as matrix A containing logical "1" (true) where the elements of A are NaNs, and logical "0" (false) where they are not (by the way, for a complex number z, isnan(z) returns true if either the real or imaginary part of z is NaN, and false if both the real and imaginary parts are finite or Inf).

Regarding your specific task, to split the original matrix into two, do the following:

TF = isnan(A);               %// Determine which elements are NaNs
nan_rows = any(TF, 2);       %// Determine rows that contain NaNs
B1 = A(nan_rows, :);         %// Rows with NaN values
B2_nonans = A(~nan_rows, :); %// Rows without NaN values