Question

I am a new Pyomo/Python user, and I am just wondering how to display the optimal variable values in a class-type Pyomo model.

I have just tried the standard example from Pyomo example library, the "min-cost-flow model". The code is available in

在代码底部，它说：

sp = MinCostFlow('nodes.csv', 'arcs.csv') 
sp.solve()
print('\n\n---------------------------')
print('Cost: ', sp.m.OBJ())

，输出为

Academic license - for non-commercial use only
Read LP format model from file.    
Reading time = 0.00 seconds
x8: 7 rows, 8 columns, 16 nonzeros
No parameters matching 'mip_tolerances_integrality' found
No parameters matching 'mip_tolerances_mipgap' found
Optimize a model with 7 rows, 8 columns and 16 nonzeros
Coefficient statistics:
  Matrix range     [1e+00, 1e+00]
  Objective range  [1e+00, 5e+00]
  Bounds range     [0e+00, 0e+00]
  RHS range        [1e+00, 1e+00]
Presolve removed 7 rows and 8 columns
Presolve time: 0.00s
Presolve: All rows and columns removed
Iteration    Objective       Primal Inf.    Dual Inf.      Time
       0    5.0000000e+00   0.000000e+00   0.000000e+00      0s

Solved in 0 iterations and 0.01 seconds
Optimal objective  5.000000000e+00

我只能得到最优目标，但是最优变量值呢？我还搜索了文档，该文档告诉我使用以下内容：

print("x[2]=",pyo.value(model.x[2])).

但它不适用于最小成本流模型之类的类类型模型。

我还试图修改该类中的函数定义：

def solve(self):
        """Solve the model."""
        solver = pyomo.opt.SolverFactory('gurobi')
        results = solver.solve(self.m, tee=True, keepfiles=False, options_string="mip_tolerances_integrality=1e-9, mip_tolerances_mipgap=0")
        print('\n\n---------------------------')
        print('First Variable: ', self.m.Y[0])

但是效果不佳。输出为：

KeyError: "Index '0' is not valid for indexed component 'Y'"

您能帮我吗？谢谢！

Gabriel

Answer 1

解决方案后显示模型结果的最直接方法是使用model.display()函数。就您而言，self.m.display()。

display()函数也适用于Var对象，因此，如果您有变量self.m.x，则可以执行self.m.x.display()。

How to display optimal variable values of a class-type Pyomo model?

1 个答案: