Objective code for summation

Answered

Musa Dursun

November 24, 2020 11:53

• 
• 
• 

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']

0

• Official comment

  

  Simranjit Kaur

  • Gurobi Staff

  June 23, 2025 03:04 Edited

  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?.
• 

  Musa Dursun

  November 24, 2020 12:09

  • 
  • 
  • 

  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)

  0
• 

  Jaromił Najman

  • Gurobi Staff

  November 24, 2020 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

  0
• 

  Musa Dursun

  November 24, 2020 14:17

  • 
  • 
  • 

  Thank you. It worked well.

  0

Post is closed for comments.