How to minimize the SUM of all flows xij

回答済み

Kaiwen Zhu

2021年11月19日 23:42

• 
• 

Hi,

How do I set the objective function to minimize the SUM of all flows xij?

My model is below,

 

import itertools
n=["a","b","c","d","e","f","g"]
arcs=list(itertools.combinations(n,2))

#model and variables
m = gp.Model('min-cost')

# create variables for arcs
x = m.addVars(arcs, vtype=GRB.CONTINUOUS, name='x')
m.update()
m.printStats()
x

#constraints
m.addConstr(x[arcs[0]]+x[arcs[1]]+x[arcs[2]]+x[arcs[3]]+x[arcs[4]]+x[arcs[5]] == 62,"c0")
m.addConstr(-(x[arcs[0]])+x[arcs[6]]+x[arcs[7]]+x[arcs[8]]+x[arcs[9]]+x[arcs[10]] == -117,"c1")
m.addConstr(-(x[arcs[1]])-(x[arcs[6]])+x[arcs[11]]+x[arcs[12]]+x[arcs[13]]+x[arcs[14]] == 81,"c2")
m.addConstr(-(x[arcs[2]])-(x[arcs[7]])-(x[arcs[11]])+x[arcs[15]]+x[arcs[16]]+x[arcs[17]] == 145,"c3")
m.addConstr(-(x[arcs[3]])-(x[arcs[8]])-(x[arcs[12]])-(x[arcs[15]])+x[arcs[18]]+x[arcs[19]] == -125,"c4")
m.addConstr(-(x[arcs[4]])-(x[arcs[9]])-(x[arcs[13]])-(x[arcs[16]])-(x[arcs[18]])+x[arcs[20]] == 105,"c5")
m.addConstr(-(x[arcs[5]])-(x[arcs[10]])-(x[arcs[14]])-(x[arcs[17]])-(x[arcs[19]])-(x[arcs[20]]) == -148,"c6")

 

m.setObjective(3*gp.quicksum(x),GRB.MINIMIZE) doesn't work.

I want my objective function to minimize 3* the sum of the flows of all arcs
something like 3*sum(xij). Any help on the syntax of this?

 

Thank you!

0

• 正式なコメント

  

  Simranjit Kaur

  • Gurobi Staff

  2025年06月23日 02:44 編集済み

  This post is more than three years old. Some information may not be up to date. For current information, please check the Gurobi Documentation or Knowledge Base. If you need more help, please create a new post in the community forum. Or why not try our AI Gurobot?.
• 

  Jaromił Najman

  • Gurobi Staff

  2021年11月22日 09:48 編集済み

  Hi Kaiwen,

  The quicksum function requires a data list as input and not just a Gurobi tupledict. Using

  m.setObjective(3*gp.quicksum(x[a] for a in arcs), GRB.MINIMIZE)

  should solve your issue.

  Best regards,
  Jaromił

  0

投稿コメントは受け付けていません。