Objective code for summation

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Musa Dursun

2020年11月24日 11:53

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I am beginner for gurobi and trying to use via python. I couldn't write a code for this summation. Would you please help me? ∑∑ t * Xkt. t and k are indices. Xkt is a binary decision variable.t is time and k consists of strings like book names. When I try to use sum or quicksum python gives error like 'unhashable list' or something like that. t = [1, 2, 3, 4, 5] k = ['k1', 'k2', 'k3', 'k4', 'k5']

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  Simranjit Kaur

  • Gurobi Staff

  2025年06月23日 03:04 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?.
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  Musa Dursun

  2020年11月24日 12:09

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  The code is as follow;

  import gurobipy as gp
  from gurobipy import GRB
  
  T = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11]
  K = ["k1","k2","k3","k4","k5","k6","k7","k8","k9"] 
  z = gp.Model("MP")
  
  x = z.addVars (T, K, vtype =GRB.BINARY, name = "jf")
  
  Job_assigns = z.addConstrs ((x.sum("*", k) == 1 for k in K), name = "job_assign")
  
  # Objective
  Result = gp.quicksum (x[T,K]*T)
  z.setObjective(Result, GRB.MINIMIZE)

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  Jaromił Najman

  • Gurobi Staff

  2020年11月24日 12:51

  Hi Musa,

  The error \(\texttt{TypeError: unhashable type: 'list'}\) means that you are trying to use a list object as an index. You are doing this at \(\texttt{x[T,K]}\) where both \(\texttt{T}\) and \(\texttt{K}\) are lists.

  You can achieve the correct summation via

  Result = gp.quicksum (x[t,k] * t for t in T for k in K)

  Best regards,
  Jaromił

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  Musa Dursun

  2020年11月24日 14:17

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  Thank you. It worked well.

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