how to convert 2*2 matrix into 256*256 matrix using for loop.

Suppose I have a matrix

b = [1 2 3
     4 5 6
     7 8 9]

and I want to extend this matrix like this

b = [ 1 2 3 1 2 3 1 2 3
      4 5 6 4 5 6 4 5 6
      7 8 9 7 8 9 7 8 9
      1 2 3 1 2 3 1 2 3
      4 5 6 4 5 6 4 5 6
      7 8 9 7 8 9 7 8 9
      1 2 3 1 2 3 1 2 3
      4 5 6 4 5 6 4 5 6
      7 8 9 7 8 9 7 8 9];

using for loop

Answer 1

[Stephen23]

Just use repmat, it is much neater and faster than using a loop:

>> b = [1,2,3;4,5,6;7,8,9]
b =
   1   2   3
   4   5   6
   7   8   9
>> R = 3;
>> C = 3;
>> repmat(b,R,C)
ans =
   1   2   3   1   2   3   1   2   3
   4   5   6   4   5   6   4   5   6
   7   8   9   7   8   9   7   8   9
   1   2   3   1   2   3   1   2   3
   4   5   6   4   5   6   4   5   6
   7   8   9   7   8   9   7   8   9
   1   2   3   1   2   3   1   2   3
   4   5   6   4   5   6   4   5   6
   7   8   9   7   8   9   7   8   9

If you really want to use a slow loop, then try this:

S = size(b);
for r = (R-1)*S(1):-S(1):0
    for c = (C-1)*S(2):-S(2):0
        out(r+1:r+S(1),c+1:c+S(2)) = b;
    end
end