多维变量的 Gurobi Python 中的 KeyError

Question

我在 Gurobi-Python 中构建了一个非常简单的优化模型，如下所示：

from gurobipy import *

commodities = ['Pencils', 'Pens']

arcs ={

  ('Detroit', 'Boston'):   100,

  ('Detroit', 'New York'):  80,

  ('Detroit', 'Seattle'):  120,

  ('Denver',  'Boston'):   120,

  ('Denver',  'New York'): 120,

  ('Denver',  'Seattle'):  120 }

# Create optimization model

m = Model('netflow')

# Create variables

flow = m.addVars(arcs,commodities)

# THE ONLY CONSTRAINT WHICH IS THE SOURCE OF ERROR!

m.addConstrs( flow[e,c] == 1 for e in arcs for c in  commodities)

# Compute optimal solution

m.optimize()

但是我得到了约束的 KeyError 。

KeyError: (('底特律', '波士顿'), '铅笔')

我看不出这个约束有什么问题。任何评论都非常感谢！

Answer 1

如果你看看你的变量：{('Detroit', 'Boston', 'Pencils'): <gurobi.Var C0>,&nbsp;('Detroit', 'Boston', 'Pens'): <gurobi.Var C1>,&nbsp;('Detroit', 'New York', 'Pencils'): <gurobi.Var C2>,&nbsp;('Detroit', 'New York', 'Pens'): <gurobi.Var C3>,&nbsp;('Detroit', 'Seattle', 'Pencils'): <gurobi.Var C4>,&nbsp;('Detroit', 'Seattle', 'Pens'): <gurobi.Var C5>,&nbsp;('Denver', 'Boston', 'Pencils'): <gurobi.Var C6>,&nbsp;('Denver', 'Boston', 'Pens'): <gurobi.Var C7>,&nbsp;('Denver', 'New York', 'Pencils'): <gurobi.Var C8>,&nbsp;('Denver', 'New York', 'Pens'): <gurobi.Var C9>,&nbsp;('Denver', 'Seattle', 'Pencils'): <gurobi.Var C10>,&nbsp;('Denver', 'Seattle', 'Pens'): <gurobi.Var C11>}你会看到你需要解开每个元组arcs：m.addConstrs( flow[e1, e2, c] == 1 for e1, e2 in arcs for c in commodities)