Jacobi method not working

Not sure what's wrong with my code. It does the first iteration correctly, then goes off in the wrong direction.

 if true
    % function x = Playing(A,b)
n = length(b);
x = zeros(1,n)';
y = x;
for k = 1:20
    for i = 1:n
        for j = 1:i-1,i+1:n
           y(i) = y(i) + A(i,j)*x(j)
        end
        y(i) = (b(i) - y(i))/A(i,i)
    end
end
end
  end

Answer 1

[Azzi Abdelmalek]

What is this: for j = 1:i-1,i+1:n ?

Maybe you mean for j = [1:i-1,i+1:n]

[Joe Smith]

I've tried both, it didn't make a difference.

[Azzi Abdelmalek]

for ii= 1:n
      s=0
      for jj = setdiff(1:n,ii)
         s = s + A(ii,jj)*y(jj);
      end
      y(ii) = (b(ii) - s)/A(ii,ii);
  end

and don't forget the initial guess y=ones(n,1) for example