我正在做一个多商品优化模型。一切正常，但是当我想在代码中添加更多约束时，我得到了错误。我想添加最后一个，其中X是发送的产品数量，D是需求。其中X应该等于或大于从i到j的需求。我该怎么解决？
我试图用不同的方式编写代码。
MODEL:
! Multi-commodity network flow problem;
SETS:
! The nodes in the network;
NODES/1..6/:;
! The set of nodes that are origins;
COMMO(NODES)/1, 2, 3, 4, 5, 6/:;
EDGES(NODES, NODES): D, C, U, V;
NET(EDGES, COMMO): X;
ENDSETS
DATA:
! Demand: amount to be shipped from
origin(row) to destination(col);
D = 0 2 4 3 0 2
0 0 2 0 1 0
0 0 0 0 0 0
0 0 0 0 0 0
0 2 0 1 0 4
0 0 0 0 0 0;
! Cost per unit shipped over a arc/link;
C = 0 2 3 4 4 4
2 0 2 1 2 3
2 1 0 1 2 2
3 2 2 0 2 2
4 2 1 3 0 1
4 3 2 3 3 0;
! Upper limit on amount shipped on each link;
U = 3 2 2 1 1 10
0 5 1 4 2 4
2 0 0 1 2 4
3 3 5 2 4 3
1 0 1 7 3 2
2 2 3 1 2 6;
! Whether an arc/link exists or not;
! V = 0 if U = 0;
! V = 1 otherwise;
V = 0 1 1 1 1 1
0 0 1 1 1 1
1 0 0 1 1 1
1 1 1 0 1 1
1 0 1 1 0 1
1 1 1 1 1 0;
ENDDATA
! Minimize ;
MIN = @SUM( NET(I, J, K): C(I, J) * X(I, J, K));
@FOR(COMMO(K): @FOR(NODES(J)|J #NE# K:
@SUM(NODES(I): V(I, J) * X(I, J, K) - V(J, I) * X(J, I, K))
= D(K, J);
);
@FOR(NODES(J)|J #EQ# K:
@SUM(NODES(I): V(I, J) * X(I, J, K) - V(J, I) * X(J, I, K))
= -@SUM( NODES(L): D(K, L))););
! Constraint;
!The amount of resources shipped over
link i to j have to be equal to or lower than the capacity;
@FOR(EDGES(I, J)|I #NE# J:
@SUM(COMMO(K): X(I, J, K)) <= U(I, J);
);
@FOR(EDGES(I, J)|I #NE# J:
@SUM(COMMO(K): X(I, J, K)) => D(I, J);
);
END
预期结果是获得优化模型。