Filling missing points in a grid

Hi everyone

I am wondering if anyone can help to mark the missing points on the grid with (x) . I have a regular points in x,y that I get from executing the differences between a predeifined points to get the grid, at the same time, some points are missing and I want to mark them (x red) as shown in the figure (i.e, (7,8), and the other missing points. How to select specific range of points with their index as marked in the black sqaure .

I have execute the code

M=3; N=4;
  mN=[0:M-1]*N;
  nM=[0:N-1]*M;
[xx yy]=meshgrid(mN, mN);
[x y]=meshgrid(nM, nM);
L1=[xx(:),yy(:)]; 
L2=[x(:),y(:)];
LL=[0,0];
 L1= union(L1, L2, 'rows');
 S=union(L1,LL,'rows');
 figure
 plot(S(:, 1),S(:,2) ,'o','color', 'b', 'markersize',4, 'linewidt',1);
LEN_S = size(S, 1);
MAX_x = max(S(:, 1));
    MIN_x = min(S(:, 1));
    MAX_y = max(S(:, 2));
    MIN_y = min(S(:, 2));
    [mx_mat, my_mat] = ndgrid(-(MAX_x - MIN_x):(MAX_x - MIN_x), -(MAX_y - MIN_y):(MAX_y - MIN_y));
    mx_vec = mx_mat(:); my_vec = my_mat(:);
    w = zeros(size(mx_vec));
    n1 = cell(size(mx_vec));
    n2 = cell(size(mx_vec));
    for ii = 1 : size(S, 1)
        for jj = 1 : size(S, 1)
            index = (mx_vec == S(ii, 1) - S(jj, 1) & my_vec == S(ii, 2) - S(jj, 2));
            w( index ) = w( index ) + 1;
            n1{ index } = [n1{ index }; S(ii, :)];
            n2{ index } = [n2{ index }; S(jj, :)];
        end
    end
    D = [mx_vec, my_vec];
    LEN_S = size(S, 1);
SS = repmat(S, [LEN_S, 1]);
SS_= kron(S, ones(LEN_S, 1));
[D1, ~, ind_SS] = unique(SS - SS_, 'rows', 'sorted');
fh2= figure (2);
 plot(D1(:,1), D1(:,2) ,'square','color', 'r', 'markersize',5, 'linewidt',2);hold on
 plot(D1(:,1), D1(:,2) ,'square','color', 'b', 'markersize',5, 'linewidt',2);hold on
 axis([-inf inf -inf inf ]);

I apperciate any help

Thanks

Answer 1

[Doddy Kastanya]

You could try to add the following at the end of your code:

hold on
text(7,8,'X','color','r')

If there are other points, then you could embed this in a for loop identifying the appropriate x and y position.