Question

I want to store data coming from for-loops in an array. How can I do that?
sample output:

for x=1:100
    for y=1:100

        Diff(x,y) = B(x,y)-C(x,y);

        if (Diff(x,y) ~= 0)

            % I want to store these values of coordinates in array
            % and find x-max,x-min,y-max,y-min
            fprintf('(%d,%d)\n',x,y);


        end
    end
end

Can anybody please tell me how can i do that. Thanks

Marry

Answer 1

So you want lists of the x and y (or row and column) coordinates at which B and C are different. I assume B and C are matrices. First, you should vectorize your code to get rid of the loops, and second, use the find() function:

Diff = B - C;  % vectorized, loops over indices automatically
[list_x, list_y] = find(Diff~=0);  
   % finds the row and column indices at which Diff~=0 is true

Or, even shorter,

[list_x, list_y] = find(B~=C);

Remember that the first index in matlab is the row of the matrix, and the second index is the column; if you tried to visualize your matrices B or C or Diff by using imagesc, say, what you’re calling the X coordinate would actually be displayed in the vertical direction, and what you’re calling the Y coordinate would be displayed in the horizontal direction. To be a little more clear, you could say instead

[list_rows, list_cols] = find(B~=C);

To then find the maximum and minimum, use

maxrow = max(list_rows);
minrow = min(list_rows);

and likewise for list_cols.