LINGO程序中@sum中@for的问题

[hm315]

代码部分：
max=@sum(link(i,j):w(i)*q(i,j)*Z(i,j))/@sum(supply(j):1000*x(j));


@for(supply(j):@sum(demand(i):Z(i,j))=1);
@for(link(i,j):Z(i,j)<=x(j));
!@for(link(i,j):Z(i,j)>0);
@for(demand(i):@sum(@for(supply(j):q(i,j)*z(i,j))))>=0.01;
@for(demand(i):@sum(supply(j):w(i)*Z(i,j))<=1000);
@for(link(i,j):@bin(Z(i,j)));
@for(supply(j):@bin(x(j)));

为什么不能再@sum中套用@for，而且在@for中套用@min也不行啊！！！
高人求解啊~！@@@