gurobi - 错误代码 = 10004 无法检索属性“X”

Question

我的 c++/gurobi 文件出现错误：

错误代码 = 10004 无法检索属性“X”

我读到这可能与标签有关？但我看不出有什么问题。 它适用于某些输入文件，但不适用于其他文件。所以我在附件中创建了一个玩具文件 t5.txt。此文件不起作用，但删除最后一列并将 8 设置为 7 可以修复它。我很困惑……

下面是model.write的输出。一切似乎都有道理，任何想法我做错了什么？ 每当我做一个model.write(test.sol)时，程序就会停止，所以解决方案似乎有问题>

附件： main.cpp -> https://dl.dropboxusercontent.com/u/13564139/main.cpp

input.txt -> https://dl.dropboxusercontent.com/u/13564139/t5.txt

Maximize
  15 student_has_projects4.1
Subject To
 R0: student_has_projects0.0 + student_has_projects1.0
   + student_has_projects2.0 + student_has_projects3.0
   + student_has_projects4.0 + student_has_projects5.0
   + student_has_projects6.0 + student_has_projects7.0 <= 4
 R1: student_has_projects1.0 + student_has_projects2.0 >= 1
 R2: student_has_projects2.0 + 2 student_has_projects5.0 <= 2
 R3: student_has_projects2.0 + 2 student_has_projects5.0 >= 1
 R4: student_has_projects0.0 + student_has_projects3.0
   + student_has_projects4.0 + student_has_projects6.0
   + student_has_projects7.0 >= 1
 R5: student_has_projects2.0 + student_has_projects5.0 <= 1
 R6: student_has_projects0.1 + student_has_projects1.1
   + student_has_projects2.1 + student_has_projects3.1
   + student_has_projects4.1 + student_has_projects5.1
   + student_has_projects6.1 + student_has_projects7.1 <= 4
 R7: student_has_projects1.1 + student_has_projects2.1 >= 1
 R8: student_has_projects2.1 + 2 student_has_projects5.1 <= 2
 R9: student_has_projects2.1 + 2 student_has_projects5.1 >= 1
 R10: student_has_projects0.1 + student_has_projects3.1
   + student_has_projects4.1 + student_has_projects6.1
   + student_has_projects7.1 >= 1
 R11: student_has_projects2.1 + student_has_projects5.1 <= 1
 R12: student_has_projects0.2 + student_has_projects1.2
   + student_has_projects2.2 + student_has_projects3.2
   + student_has_projects4.2 + student_has_projects5.2
   + student_has_projects6.2 + student_has_projects7.2 <= 4
 R13: student_has_projects1.2 + student_has_projects2.2 >= 1
 R14: student_has_projects2.2 + 2 student_has_projects5.2 <= 2
 R15: student_has_projects2.2 + 2 student_has_projects5.2 >= 1
 R16: student_has_projects0.2 + student_has_projects3.2
   + student_has_projects4.2 + student_has_projects6.2
   + student_has_projects7.2 >= 1
 R17: student_has_projects2.2 + student_has_projects5.2 <= 1
 R18: student_has_projects0.0 + student_has_projects0.1
   + student_has_projects0.2 = 1
 R19: student_has_projects1.0 + student_has_projects1.1
   + student_has_projects1.2 = 1
 R20: student_has_projects2.0 + student_has_projects2.1
   + student_has_projects2.2 = 1
 R21: student_has_projects3.0 + student_has_projects3.1
   + student_has_projects3.2 = 1
 R22: student_has_projects4.0 + student_has_projects4.1
   + student_has_projects4.2 = 1
 R23: student_has_projects5.0 + student_has_projects5.1
   + student_has_projects5.2 = 1
 R24: student_has_projects6.0 + student_has_projects6.1
   + student_has_projects6.2 = 1
 R25: student_has_projects7.0 + student_has_projects7.1
   + student_has_projects7.2 = 1
Bounds
Binaries
 student_has_projects0.0 student_has_projects0.1 student_has_projects0.2
 student_has_projects1.0 student_has_projects1.1 student_has_projects1.2
 student_has_projects2.0 student_has_projects2.1 student_has_projects2.2
 student_has_projects3.0 student_has_projects3.1 student_has_projects3.2
 student_has_projects4.0 student_has_projects4.1 student_has_projects4.2
 student_has_projects5.0 student_has_projects5.1 student_has_projects5.2
 student_has_projects6.0 student_has_projects6.1 student_has_projects6.2
 student_has_projects7.0 student_has_projects7.1 student_has_projects7.2
End

Answer 1

问题是您的 lp 实例不可行，因此对 .optimize() 的调用会导致不可行状态。来自您的代码

model.write("test2.lp");
model.optimize();
model.write("forum2.sol");

if(model.get(GRB_IntAttr_Status) != GRB_OPTIMAL){
    cout << "niet optimaal " << endl;
}

在检查是否成功之前，您正在编写一个 .sol 文件。 Gurobi 在写入 .sol 文件时从变量中获取“X”属性。如果优化失败，则“X”属性不可用并引发异常。在编写 .sol 文件或获取许多属性（包括“X”、“Pi”和“ObjVal”）之前，您应该确保 gurobi 有解决方案。 OPTIMAL status codes 向您保证有一个可用的解决方案，但是像 SUBOPTIMAL 这样的代码也表明有一个可用的解决方案，而其他像 TIME_LIMIT、NODE_LIMIT 这样的代码意味着可能有一个可用的解决方案。您可以获取属性SolCount 以明确指示是否有可用的解决方案。

您的问题实例不可行，因为约束（R1、R7、R13 意味着学生 1 和 2 至少需要 3 个项目，但约束（R19、R20）意味着他们每个人只能有 1 个项目。您可以通过以下方式查看使用 IIS 求解器。在交互式 gurobi 中，您可以获得 Irreducible Inconsistent Subsystem

m = read("test2.lp")
m.optimize()
m.computeIIS()
m.write("test2.ilp")