字典模型的问题 - CPLEX OPL - 模型永远运行而没有答案答案

【问题标题】：Problem with lexicographic model - CPLEX OPL - Model is running forever with no answer字典模型的问题 - CPLEX OPL - 模型永远运行而没有答案
【发布时间】：2020-02-24 12:18:05
【问题描述】：

我在 1:31 分钟停止，这是引擎日志输出：我正在使用 CP 制作模型以进行目标编程 - 字典。数据来自一个excel文件。问题是：软件正在运行，正在运行....没有答案。我可以看到它正在工作，因为时间在右下角过去。数据不是太大，我在 CPLEX 的其他分析中使用了相同的数据，效果很好。

Excel 文件： https://drive.google.com/open?id=1rOKhqlegKo-BHJnJj9cnnpKMdwpktYlX

1) 有人能看出什么问题吗？ 2）只要确保，使用 CP 不可能将 dvar 作为 float+，对吗？

谢谢

.mod

 using CP;
 // variable decision 

 {string} Forest = ...;
 {string} Products = ...;
 {string} Destination = ...;

 float Demand [Destination][Products]= ...; //volume in Kg
 float Distance [Forest][Destination]= ...; //in Km
 float Stock [Forest][Products]= ...; //volume in Kg 
 float Freshness [Forest][Products]=...; `


 //Decision Variables
 dvar int+ Delivered [Forest][Destination][Products];

 //Expressoes
 dexpr float Opt_Distance = sum (u in Forest, c in Destination, p in Products) Distance[u][c] * Delivered[u][c][p]; 
 dexpr float Opt_Freshness =  sum (u in Forest, c in Destination, p in Products) Freshness[u][p] * Delivered[u][c][p]; 

 //Objective Function
 minimize staticLex (Opt_Distance,Opt_Freshness); 


 //Constraint
 subject to {
     forall (p in Products)
         forall (u in Forest)
             sum (c in Destination)
                 Delivered[u][c][p] <= Stock [u][p];

     forall (p in Products)
         forall (c in Destination)
             sum (u in Forest) 
                 Delivered[u][c][p] >= Demand[c][p];

}

.dat

 // variable decision 

 Forest = {"F1","F2","F3","F4","F5","F6","F7","F8","F9","F10","F11","F12","F13","F14","F15","F16","F17","F18","F19","F20","F21","F22","F23","F24","F25","F26","F27","F28","F29","F30","F31","F32","F33","F34","F35","F36","F37","F38","F39","F40","F41","F42","F43","F44","F45","F46","F47","F48","F49","F50"};
 Products = {"P1","P2","P3","P4"};
 Destination = {"D1","D2","D3","D4","D5","D6","D7","D8","D9","D10"};



 SheetConnection sheet("...Data_test.xlsx");


 Demand from SheetRead(sheet,"Demand");
 Distance from SheetRead(sheet,"Distance");
 Stock from SheetRead(sheet,"Stock");
 Freshness from SheetRead(sheet,"Freshness");

【问题讨论】：

您至少应该将引擎日志输出添加到您的帖子中。否则无法判断可能发生的情况。如果您还可以添加 Excel 电子表格，我们可以尝试在此处运行您的模型。这可能会更清楚地说明正在发生的事情。
你能澄清一下到底是什么问题吗？从引擎输出我们可以看到求解器找到了许多可行的解决方案，然后手动中断。所以它确实找到了一些东西。它只是无法证明最优性。这可能需要任意时间（参见 Petr 的回答）。

标签： cplex opl lexicographic

【解决方案1】：

您似乎没有设置任何时间限制。在这种情况下，引擎会搜索最佳解决方案，直到它可以证明当前解决方案是最佳的。一般来说，不能保证搜索会在合理的时间内结束（问题可能是 NP）。

如日志所示，您在 88 秒后手动停止了搜索（“通过中止”），同时找到了 86 个解决方案。每次找到解决方案时，日志中都会有一行以星号开头。当前的最佳目标值也打印在日志中（第一列）。

所以我建议在您的模型中添加一些时间限制（或其他类型的限制）。可以这样做：

execute {
  cp.param.timelimit = 120; // In seconds 
}

是的，CP 模型中不可能有浮点变量。

【讨论】：