AMPL:下标

Question

你好，各位乐观主义者！

我对以下约束有一些问题：

#The supply at node i equals what was present at the last time period + any new supply and      subtracted by what has been extracted from the node.    
subject to Constraint1 {i in I, t in T, c in C}:
    l[i,t-1,c] + splus[i,t] - sum{j in J, v in V, a in A} x[i,j,v,t,c,a]= l[i,t,c];

这自然导致这个约束在它第一次循环时提供错误，因为t-1没有定义(对于我来说，li,0，c没有定义。哪里

  var l{I,T,C} >= 0;    # Supply at supply node I in time period T for company C.
  param splus{I,T};     # Additional supply at i.
  var x{N,N,V,T,C,A} integer >= 0;  #Flow from some origin within N to a destination within N using vehicle V, in time T, for company C and product A.

集合T；(在.mod中)是定义为：

 set T := 1 2 3 4 5 6 7; in the .dat file

我试过这样做：

subject to Constraint1 {i in I, t in T: t >= 2, c in C}:
all else same

这给我带来了语法错误。我还尝试为所有可能的组合包括"let 101，1 := 0“，这使我产生了错误

  error processing var l[...]:
  no data for set I

我也试过

subject to Constraint1 {i in I, t in T, p in TT: p>t, c in C}:
   l[i,t,c] + splus[i,p] - sum{j in J, v in V, a in A} x[i,j,v,p,c,a]= l[i,p,c];

哪里

set TT := 2 3 4 5 6;

在.dat文件中(仅在.mod中设置TT；)，这也会导致错误。有人知道怎么做吗？

Answer 1

解决这个问题的一种方法是在索引表达式的末尾指定条件t >= 2：

subject to Constraint1 {i in I, t in T, c in C: t >= 2}:
  ...

有关索引表达式语法的更多详细信息，请参见A.3节索引表达式和下标。