PULP - 如何获取 CPLEX 求解器状态而不是 LpStatus 状态？

Question

我在 Python 中通过 PULP 使用 CPLEX 求解器。当我解决有时间限制的问题时，CPLEX 会在屏幕上打印代码 107 which means "Time limit exceeded, but integer solution exists". However, if I print the status of pulp.LpStatus[problem.status] what I get back is the value 1 which according to pulp's documentation 表示已找到最佳解决方案，这实际上是错误的。

如何访问 CPLEX 状态代码而不是 PULP 的？

Answer 1

您可以直接访问 CPLEX 状态代码和状态字符串。考虑以下示例：

>>> import pulp 
>>> prob = pulp.LpProblem("example", pulp.LpMinimize)
>>> x = pulp.LpVariable('x', lowBound=0, upBound=1)
>>> prob+= x <= -1

• 示例 1 - 超出时间限制

  >>> solver = pulp.CPLEX_PY(msg=0, timeLimit=0)
  >>> prob.setSolver(solver)
  >>> prob.solve()
  -3
  >>> solver.solverModel.solution.get_status()
  108
  >>> solver.solverModel.solution.get_status_string()
  'time limit exceeded, no integer solution'
  

• 示例 2 - 不可行

  >>> solver = pulp.CPLEX_PY(msg=0)
  >>> prob.setSolver(solver)
  >>> prob.solve()
  -1
  >>> solver.solverModel.solution.get_status()
  103
  >>> solver.solverModel.solution.get_status_string()
  'integer infeasible'