Dear all, I encountered today that there is a possible bug when adding sparse and diagonal matrices. Here is an example A=5*sparse(eye(2))+sparse([1 2 2],[2 1 2],[-1 1 3]); B=5*eye(2)+sparse([1 2 2],[2 1 2],[-1 1 3]); full(A)-full(B) % gives [0 0; 0 0] full(A-B) % gives [-5 0; 0 0] Best regards, Sebastian Schoeps