MATLAB: Matrix addition different dimension using for loops.

for loop matrix addition

Hi,
I am trying to do matrix addition of 2*4 to fit in 4*4 matrix. I am using for loops to get me familiarize with loops so that i can use it for image matrix manupulation. But with my code my output is 2*4 instead of 4*4.. could someone explain me the concept or the logic i am lacking here .. 
a = [11:14; 15:18]; 
 b = [3 2 3 1; 2 1 1 1;1 3 3 2; 2 1 1 3];
for i = 0
    for j = 0
        for  x = 1:2
            for y = 1:4
                c(i+x,j+y) =b(i+x,j+y)+a(x+i,y+j);
            end 
        end
    end
end

Best Answer

%this code will fail if a or b is empty, or if one size is not an exact multiple of the other
asz = size(a);
bsz = size(b);
maxsz = max(asz,bsz);
arep = maxsz ./ asz;
brep = maxsz ./ bsz;
ar = repmat(a, arep);
br = repmat(b, brep);
c = ar + br;
That is, create new matrices that contain the old matrices copied as many times as needed.
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