Suppose that there are M demand nodes and N supply nodes. Let sub(d,i) be the demand at node sub(D,i), and let sub(s,i) be the supply at sub(S,i). For Solver to be able to find a solution, which of the following must be true? The total supply S=sub(s,1)+...+sub(s,N) is less than the total demand D=sub(d,1)+...+sub(d,M). i,sub(d,i)sub(s,i). (This means that for all i, the demand at node i is less than the supply at node i.) sum(sub(d,i),i=1,M)>sum(sub(s,j),J,N). The total demand D=sub(d,1)+...+sub(d,M) is equal to the total supply S=sub(s,1)+...+sub(s,N)