如何在 CPLEX python 中编写条件约束？

Question

我的模型有一个二进制变量 x [i] [j] [k]。我需要添加满足此条件的约束：


if x[i][j][k1]==1  and  x[j][i][k2]==1 

Then:

 k2-k1>8

我有这个代码，但我认为它不正确:

  mdl.add((y[(i,j,k)]+y[(j,i,k1)]==2),(k1-k>8) )

我也是，把这个：

 mdl.add(mdl.if_then(y[(i,j,k1)]+y[(j,i,k2)]==2, k2-k1>8))

但是我得到了这个错误：

    raise DOcplexException(resolved_message)

DOcplexException: Expecting linear constraint, got: False

如何使用 cplex python API 建模？

Answer 1

让我分享

中的 if then 示例

https://www.linkedin.com/pulse/making-optimization-simple-python-alex-fleischer/

from docplex.mp.model import 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()

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

print()
print("with if nb buses 40 more than 3  then nbBuses30 more than 7")

#if then constraint
mdl.add(mdl.if_then(nbbus40>=3,nbbus30>=7))
mdl.minimize(nbbus40*500 + nbbus30*400)

mdl.solve()



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

如果你想看 if

from docplex.mp.model import 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()

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

print()
print("with if nb buses 40 more than 3 and less than 7 then nbBuses30 more than 7")

#if then constraint
mdl.add(mdl.if_then((nbbus40>=3) + (nbbus40<=7)>=2,nbbus30>=7))
mdl.minimize(nbbus40*500 + nbbus30*400)

mdl.solve()



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

你也可以重写

from docplex.mp.model import 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()

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

print()
print("with if nb buses 40 more than 3 and less than 7 then nbBuses30 more than 7")

#if then constraint
mdl.add((((nbbus40>=3) + (nbbus40<=7)>=2))<=(nbbus30>=7))
mdl.minimize(nbbus40*500 + nbbus30*400)

mdl.solve()



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

Answer 2

Model.if_then 从左到右链接两个线性约束。如果第一个满意了，第二个也会满意。

在您的案例中，我了解到 k2-k1>8 不涉及任何决策变量。所以这完全取决于数据，在模型构建时已知。

在那种情况下，因果关系相反：如果 k2-k1>8，则 x[i,j,k1] 和 x[i,j,k2] 都必须等于 1。

那么最简单的代码就是：

if k2-k1>8:
   m.add(x[i,j,k1] == 1)
   m.add(x[i,j,k2] == 1)

如何在 CPLEX python 中编写条件约束？

how to write a conditional constraint in CPLEX python?

python

cplex

python-3.x

docplex