2D Convolution algorithm error vs conv2 function

    [r,c] = size(x);
    [m,n] = size(y);
    h = rot90(y, 2);
    center = floor((size(h)+1)/2);
    Rep = zeros(r + m*2-2, c + n*2-2);
    return

    for x1 = m : m+r-1
    for y1 = n : n+r-1
        Rep(x1,y1) = x(x1-m+1, y1-n+1);
    end
    end

    B = zeros(r+m-1,n+c-1);
    for x1 = 1 : r+m-1
    for y1 = 1 : n+c-1
        for i = 1 : m
            for j = 1 : n
                B(x1, y1) = B(x1, y1) + (Rep(x1+i-1, y1+j-1) * h(i, j));
            end
        end
    end
    end
    Con=conv2(Rep,h);

In this code ,after getting result of conv2 , i see that the above algorithm misses many elements of wanted output of convolution.Can someone help to fix this problem?

Answer 1

[Andrei Bobrov]

a =reshape(1:12,4,[]);
b = reshape(1:8,2,[]);

without conv2

[m,n] = size(a);
[m1,n1] = size(b);
mn = [m,n] + 2*([m1,n1]-1);
a0 = zeros(mn);
a0(m1:(end-m1+1),n1:(end-n1+1)) = a;
i0 = reshape(1:numel(a0),mn(1),[]);
ii = i0(1:end-m1+1,1:end-n1+1);
i1 = bsxfun(@plus,(0:m1-1)',(0:n1-1)*mn(1));
idx = bsxfun(@plus,ii(:),i1(:)');
out = reshape(a0(idx)*reshape(rot90(b,2),[],1),m1+m -1,[]);

without conv2, with for loops

[m,n] = size(a);
[m1,n1] = size(b);
mn = [m,n] + 2*([m1,n1]-1);
a0 = zeros(mn);
a0(m1:(end-m1+1),n1:(end-n1+1)) = a;
b1 = rot90(b,2);
b2 = b1(:);
out = zeros(m1+m-1,n+n1-1);

for ii = 1:mn(1)-m1+1
    for jj =  1:mn(2)-n1+1
        x = a0(ii:ii+m1-1,jj:jj+n1-1);
        out(ii,jj) = x(:)'*b2;
    end
end

with conv2

out = conv2(a,b)

[billy papas]

Thanks for the answer.But would like to optimize my code so that i can work.Your code seems really complex for my knowledge,although it's excellent as implementation.