C = sparse(9,9);
C(1,2) = 6;
C(1,4) = 8;
C(2,3) = 1;
C(2,5) = 1;
C(3,6) = 1;
C(4,3) = 1;
C(4,5) = 1;
C(5,6) = 1;
C(6,7) = 1;
C(6,8) = 1;
C(7,8) = 1;
C(7,9) = 1;
C(8,9) = 1;