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我有一个关于 docplex 库的基本问题。有谁知道从现有模型中添加/删除变量的最佳方法是什么？我正在使用以下代码来创建决策变量

self.model.continuous_var_dict(self.N, lb=0)

我可以通过增加 的大小来再次运行这条线self.N吗？

我还想知道是否有更新现有约束的有效方法，现在，我正在删除所有约束并使用以下代码添加新约束

self.model.remove_constraints(self.constrains)
self.constrains = self.model.add_constraints(
        self.model.sum(self.cons_coef[(i, k, p)] * self.x_mp[(k, p)] for k, p in self.N) == 1 for i in range(N))

如果我只想在列生成中添加新列怎么办？

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2 回答 2

0

您可以进行增量更改：

 from docplex.mp.model import Model

# original model

mdl = Model(name='buses')
nbbus40 = mdl.integer_var(name='nbBus40')
nbbus30 = mdl.integer_var(name='nbBus30')
mdl.add_constraint(nbbus40*40 + nbbus30*30 >= 300, 'kids')
mdl.minimize(nbbus40*500 + nbbus30*400)

mdl.solve()

mdl.export("c:\\buses.lp")

for v in mdl.iter_integer_vars():
    print(v," = ",v.solution_value)

#now 350 kids instead of 300

print()
print("now 350 kids instead of 300")    

mdl.get_constraint_by_name("kids").rhs=350;
mdl.solve()

for v in mdl.iter_integer_vars():
    print(v," = ",v.solution_value)

# no more than 4 buses 40 seats

print()
print("no more than 4 buses 40 seats")


mdl.get_var_by_name("nbBus40").ub=4
mdl.solve()

for v in mdl.iter_integer_vars():
    print(v," = ",v.solution_value)

#change the objective so that cost for 40 seats is 450
#and remove the limit on the number of buses 40 seats

print()
print("change the objective so that cost for 40 seats is 450")
print("and remove the limit on the number of buses 40 seats  ")  

mdl.get_var_by_name("nbBus40").ub=1000
mdl.set_objective("min",nbbus40*450 + nbbus30*400);
mdl.solve()

for v in mdl.iter_integer_vars():
    print(v," = ",v.solution_value)

这使

nbBus40  =  6.0
nbBus30  =  2.0

now 350 kids instead of 300
nbBus40  =  8.0
nbBus30  =  1.0

no more than 4 buses 40 seats
nbBus40  =  2.0
nbBus30  =  9.0

change the objective so that cost for 40 seats is 450
and remove the limit on the number of buses 40 seats  
nbBus40  =  8.0
nbBus30  =  1.0
于 2019-11-13T14:31:24.500 回答
0

添加变量的方式（通过Continuous_var_dict）很好。是的，您可以continuous_var_dict重复调用以添加几批变量。就性能而言，docplex应该以尽可能快的方式将这些添加到 CPLEX。如果您对性能缓慢感到惊讶，请分享具体信息。

要删除变量，请将它们从模型的目标和约束中删除。例如，使用LinearExpr.remove_term。

要修改约束，您可以执行以下操作（请参阅LinearConstraint.lhs）：

for c in contraints:
   c.lhs += model.sum_vars(newvars)

“docplex增量建模”示例演示了这一点（参见此处）。

于 2019-11-14T18:03:08.023 回答