Gurobipy 问题：无法将 IIS 写入 .ilp 文件

Question

我们正在使用 Gurobipy（来自其 Gurobi 云产品）。我们正在利用其 IIS feature 来处理不可行性调试。

但是 Gurobipy 无法将 IIS 写入 .ilp 文件（即生成一个完全空的文件）。

下面是最小的可重现代码：

main.py

import gurobipy

my_model = gurobipy.read("my_problem.lp", conf_env())  
# Note: conf_env() is custom func to set secret key

my_model.optimize()
my_model.computeIIS()         
my_model.write('my_iis.ilp')   # Generates an empty file: my_iis.ilp

my_problem.lp

\ENCODING=ISO-8859-1
\Problem name:

Minimize
 obj: x1 + x2
Subject To
 c1: - x1 <= -20
 c2: - x2 <= -20
 c3: - x1 <= -60
 c4: - x2 <= -60
 c5: x1 + x2 <= 110
Bounds
      x1 Free
      x2 Free
End

Answer 1

在我的机器上（同时使用 Gurobi 云和本地优化）您的代码运行良好并生成此 ILP 文件：

Minimize
 
Subject To
 c3: - x1 <= -60
 c4: - x2 <= -60
 c5: x1 + x2 <= 110
Bounds
 x1 free
 x2 free
End

这是对应的输出：

Using license file C:\gurobi\gurobi.lic
Read LP format model from file inf.lp
Reading time = 0.00 seconds
obj: 5 rows, 2 columns, 6 nonzeros
Gurobi Optimizer version 9.1.2 build v9.1.2rc0 (win64)
Thread count: 4 physical cores, 8 logical processors, using up to 8 threads
Optimize a model with 5 rows, 2 columns and 6 nonzeros
Model fingerprint: 0xd8caa76c
Coefficient statistics:
  Matrix range     [1e+00, 1e+00]
  Objective range  [1e+00, 1e+00]
  Bounds range     [0e+00, 0e+00]
  RHS range        [2e+01, 1e+02]
Presolve removed 4 rows and 2 columns
Presolve time: 0.00s

Solved in 0 iterations and 0.00 seconds
Infeasible or unbounded model
Iteration    Objective       Primal Inf.    Dual Inf.      Time
       0      handle free variables                          0s

IIS computed: 3 constraints and 0 bounds
IIS runtime: 0.00 seconds

你的设置一定有问题，因为代码和模型文件都是正确的。您应该检查解算器输出是否有任何线索。

编辑：

更新 Gurobi 解决了这个问题。

Gurobipy 问题：无法将 IIS 写入 .ilp 文件

Gurobipy issue: fails to write IIS to .ilp file

python

gurobi